Add kernel-style events for sched_trace_XXX() functions

Enable kernel-style events (tracepoint) for Litmus. Litmus events
trace the same functions as the sched_trace_XXX(), but can be
enabled independently.

So, why another tracing infrastructure then:
- Litmus tracepoints can be recorded and analyzed together (single
  time reference) with all other kernel tracing events (e.g.,
  sched:sched_switch, etc.). It's easier to correlate the effects
  of kernel events on litmus tasks.

- It enables a quick way to visualize and process schedule traces
  using trace-cmd utility and kernelshark visualizer.
  Kernelshark lacks unit-trace's schedule-correctness checks, but
  it enables a fast view of schedule traces and it has several
  filtering options (for all kernel events, not only Litmus').
An efficient binary heap implementation.

An efficient binary heap implementation coded in the
style of Linux's list.  This binary heap should be able
to replace any partially sorted priority queue based
upon Linux's list.
Move budget-related helpers to budget.h

litmus.h is accumulating too many things. Since
we already have budget.h, let's stick all budget-related
inline functions there as well.

This patch is merely cosmetic; it does not change
how budget enforcement works.
GSN-EDF: do not requeue jobs without budget

This patch changes how preemptions of jobs without
budget work. Instead of requeuing them, they are now
only added if they are not subject to budget enforcement
or if they have non-zero budget. This allows us to process
job completions that race with preemptions.

This appears to fix a BUG in budget.c:65 reported by Giovani Gracioli.
C-EDF: do not requeue jobs without budget

This patch replicates the fix in commit
f141d730e91283a9bb5cfcb134fcead55d5da0c6
(which applies to GSN-EDF).
Update to improved x86 Feather-Trace triggers

This patch imports recent upstream changes in Feather-Trace that reduce
register pressure around Feather-Trace triggers.

References: Commits 00713b8 and 225d734 in Feather-Trace.

    https://github.com/brandenburg/feather-trace/commit/00713b878636867ce07291c588509b38fa5bf152
    https://github.com/brandenburg/feather-trace/commit/225d7348a08682cd87f72b127142bdfd6c0c7890
P-FP: port P-FP plugin used in B. Brandenburg's
      dissertation (branch bbb-diss) to current
      version of litmus

This is needed for ongoing projects

I took the unchanged code but removed some leftovers
of OMLP which is not implemented
P-FP: make PCP available to userspace

Prior to that it was only used internally for DPCP
P-FP: fix build bug if !CONFIG_RELEASE_MASTER

Move declaration of 'cpu' out of #ifdef block, it's also needed for
CONFIG_LITMUS_LOCKING.
P-FP: Clarify meaning of priorities

Add a comment to explain how priorities are
interpreted, and provide some useful macros for
userspace.
P-FP: reject tasks with invalid priorities

The existing admission test failed to test for too-low
priorities. Use the common macro to accept only valid
priorities.
control page: use vm_insert_page() instead of remap_pfn_range()

vm_insert_page() is the simpler and preferred interface for remapping
individual pages and includes additional error checks. It suffices for
our purposes, so let's use it instead.
control page: warn on page fault

Page faults should not happen here.  Scream if they do anyway. This is
useful when extending the control page.
control page: avoid "minor" page faults

By default, even private writable pages are mapped
with the RW bit disabled in the PTE. This causes a
"minor" page fault when the page is first written
to. To avoid this, make sure that vm_inert_page()
uses the proper page protection bits and mark the
VMA as VM_IO to keep the rest of the VM code out.
New Feature: Arbitrary deadlines.

Added support for arbitrary deadlines.

Constraint: Relative deadline must be >= exec cost.

Use: Set relative deadline in rt_task::rdeadline. Set value to 0
     to default to implicit deadlines.

Limitations: PFAIR not supported by this patch. PFAIR updated to
     reject tasks that do not have implicit deadlines.