Increase slab-block size in signal component

The backend allocator for the slab is a sliced heap, which hands out
allocations with page-size granularity (4096 bytes). Therefore, the
slab-block size should also be about a multiple of the page size minus
some bytes of overhead.

Additional adjustments:

- The slab-block size and the default quota-upgrade amount for SIGNAL
  sessions depends on the platform bit width now.
- The signal test also stresses the case of many managed context in one
  session including creation and destruction of the used signal receiver
  in repeated rounds.
hw: set TTBR0 according to CPU facilities

Fixes #1195
Add 'check_tool' function to new ports mechanism

Fixes #1254.
libports: fix sdl_mixer include paths

Fixes #1255.
hw: correctly flush cache on ARM (fix #1257)

* When flushing the data and unified cache on ARM, clean and invalidate
  instead of just cleaning the corresponding cache lines
* After zero-ing a freshly constructed dataspace in core, invalidate
  corresponding cache lines from the instruction cache
Input merger

This component merges the input events of multiple sources.

Example configuration:

<start name="input_merger">
	<resource name="RAM" quantum="1M" />
	<provides>
		<service name="Input" />
	</provides>
	<config>
		<input label="ps2" />
		<input label="usb_hid" />
	</config>
	<route>
		<service name="Input">
			<if-arg key="label" value="ps2" /> <child name="ps2_drv" />
		</service>
		<service name="Input">
			<if-arg key="label" value="usb_hid" /> <child name="usb_drv" />
		</service>
		<any-service> <parent /> <any-child /> </any-service>
	</route>
</start>

For each 'input' config node, the component opens an 'Input' session with the
configured label. This label is then evaluated by 'init' to route the session
request to a specific input source component.

Fixes #1259.
ps2_drv: read configuration before self tests

It turned out that the controller configuration can change during the self
tests, so now it is read before running the tests and restored afterwards.

Fixes #1260.
seoul: update branch to using vbios emulators

* use seoul branch containing vbios emulator

* report the memory model in the VBE mode info as otherwise the
  Genode framebuffer driver will ignore this mode

Fixes #1261
iso9660: remove on-demand paging

Required to run a Genode VM provided as ISO - issue #1261
ahci: ignore spurious interrupts

Qemu 2.0 makes trouble when using seoul-disc.run - related to #1261
seoul: add script turning Genode scenario into VM

Related to issue #1261
seoul: use pae branch of seoul

Fixes #1262
VESA driver: choose highest resolution video mode

With this patch, the VESA driver chooses the video mode with the highest
resolution from the list of available modes if no resolution is
explicitly configured.

Fixes #1263.
VESA driver: typo fix

Fixes #1265.
nova: handle race during signal setup phase

Fixes #1266
Heap: release some memory to the RAM session

With this patch, allocations >= 64K are fulfilled by dedicated
dataspaces, which are released to the RAM session when not needed
anymore.

Fixes #1267
Qt5: support window resizing by window manager

Fixes #1268
xml_generator: timer not needed for test
fixup "vfs: use 64bit for file offset and size"
run: mark ext2 partition as bootable

When building for the 'disk' run target, the ext2 partition needs to be
marked as bootable to be booted from on some hardware.

Fixes #1270