dde_linux: Support for Raspberry Pi

At the current stage, the USB HID and storage drivers are prinicpally
working but not stable. If interrupts are not processed fast enough,
devices will get sporadically disconnected.
HACK to enable PMU in base-hw for Raspberry Pi
thread: convenience trace methods

Implementation of declared trace methods for (null-temrinated) C string
and character buffer with given length.
base-hw: Pic::mask for rpi
dde_kit: Allow re-scheduling from timer handler

Prior this change, the attempt to re-schedule a timer from its timer
handler resulted in a clear '_pending' flag. This caused the timer event
to disappear from the scheduling queue without the handler being called
ever again. By resetting the '_pending' value before calling the hander,
we prevent a re-scheduled '_pending' flag to be cleared immediately
after calling the handler.
trace: Frontend for reading trace-buffer entries
attached_mmio: Support sub-page MMIO resources
dde_linux: Disable IRQ batching (temporary)
dde_linux: Fix MAC validity check
rpi: Videocore cache definitions
dde_linux: USB networking for rpi
dde_linux/rpi: MPHI definitions (WiP)
rpi: Change link address to support larger images
base-hw: Eager scheduling of IRQ handlers (WiP)
Move generic platform_session parts to os/include

Both 'platform_session/capability.h' and 'platform_session/connection.h'
do not contain platform-specific information. By moving them from
'include/platform/imx53/platform_session/' to 'include/platform_session/',
this patch enables other platforms to reuse them.
Place crt0 at beginning of the first ELF segment

This patch make sure that ELF entry corresponds to the start of the
first segment. This way, we can easily create a raw binary from an
ELF image using objcopy, and simply start the execution at the start
of the raw binary. Patch by Christian Helmuth.
Tracing of USB HID interrupts on Raspberry Pi
rpi: Allow the access to videocore memory as MMIO
rpi: Framebuffer and platform drivers

The platform driver is used to access the features provided by the
Videocore mboxes, i.e., power configuration and framebuffer setup. The
framebuffer driver uses the platform interface to setup a screen mode of
1024x768.
dde_linux/rpi: Enable USB power on startup

Needed when booting Genode directly from SD card w/o u-boot.