Document flags of vm_page allocation functions.

Reviewed by:	alc
Do not clear flag that vm_page_alloc() doesn't support.

Submitted by:	kib
Add flag VM_ALLOC_NOWAIT for vm_page_grab() that prevents sleeping and
allows the function to fail.

Reviewed by:	kib, alc
Sponsored by:	Nginx, Inc.
Minimize usage of leaked definitions from pte.h
Rename pmap_kenter_temp() to commonly used pmap_kenter_temporary().
Note: minidump still needs next cleanup.
Cleanup switch.S. Simplify frame structures used in system.
Simplify TLS handling.
Since TLS pointer cannot be changed directly from userland is not necessary to save it on each task switch.
Define new inline TLB and cache functions.
Cleanup exception.S. Prepare for later unification of data_abort_handler() and prefetch_abort_handler().
First step in cleanup of locore.S. Fix initial stack allocation. Rename initial page table and use it for startup of secondary cores too. Same page table can be used for CPU hot plug and/or power management later.
Add new ARMv6 specific trap-v6.c.
Add new pmap code.
Fix handling of direct section unmapping.
    Use local variant of tlb_fush functions where appropriate
Merge r271716
Implement initial version of cpuinfo.
Rename pmap_tlb_flush_page. Use correct argument type  when calling tlb_flush functions. Minor cleanup nits.
Switch DMA coherent memory to normal uncacheable memory
Major cleanup of new pmap code.
Fix comments. Use macro for simplify pvh list Add first managed physical address.
Fix style.
Use new VM_PHYSSEG_SPARSE infrastructure