ports: common utilities for building VMMs on NOVA

To ease the creation of custom virtual machine monitors on top of
NOVA, this patch moves generic utilities from vancouver resp. seoul to the
public include location 'ports/include/vmm'. As a nice side effect,
this change simplifies 'vancouver/main.cc'.

Issue #949
nova: support creation of vCPU in own PD

With the patch a VMM is not forced anymore to co-located the VMM and VM in same
PD.

Fixes #949
seoul: support to run VM outside VMM's PD

Issue #949

Related to issue #808 - one way to nearly double the maximum VM size for
VMs on 32bit Genode/Nova host if decreased performance is acceptable.
netperf: remove packet/s from statistics

Mixing MB/s and packet/s in one graph is a bit confusing - so remove it from
the graph, but is still in the log output.
block_session: extend interface with sync() call

To support components, which implement the block session's server side
rpc object, and which doesn't write data to their device backend immediately,
an additional synchronization call is needed. Thereby, clients like for
instance a file system can tell these components, when a synchronization is
required.

Ref #113
base: Local signal submit
lxip: Port of the Linux TCP/IP stack
make dde_linux repository an optional one

Since dde_linux now contains the port of the Linux IP stack available for all
Genode base-* platforms move the repository out of drivers_arm and drivers_x86
build.conf to the optional build.conf (available to all platforms).
netperf: Add separate run scripts for lwip/lxip

Also removed target 'app/netperf' and added 'app/netperf/lwip' and
'app/netperf/lxip'.
libports: libc_block plugin

This plugin provides support for using a Block_session connection by
opening "/dev/blkdev".

Fixes #965.
libports: add sys/disk.h symlink

Fixes #965.
Fix some typos
ram_fs: use server skeleton library

Related to #944.
base-linux: hybrid file-system server

The current implementation is missing support for symbolic links.

Fixes #944.
gpio_drv: Fix linking on PandaBoard

Issue #708
usb_drv: Use GPIO driver on PandaBoard

Also updated run scripts.

Issue #708
cpu_session: follow-up fix for scale_priority

This is a fixup for commit 5a42f40f04981581327639a75298e9e653ef39f5.

ref #961
base: Warn on undissolved signal contexts
Dissolve sig contexts in rm_fault and signal tests
hw: no default values for kernel-call args

ref #967