Fix usb driver configuartion in l4linux run script

Don't use the xhci USB host controller for HID and NIC in the l4linux
run script. It doesn't work on the Pandaboard, and isn't needed for the
Arndale board. Moreover, provide a MAC address, and add a providing
rule in the KDB UART driver to supress ugly warnings. Fix #763
Add print-only dummy UART driver for Exynos5 SoC

Fix #759
Don't abort when reading config in OMAP4 fb driver

Just use configuration values when existent, otherwise when no configuration
is given use the default values. When an incomplete configuration is given,
take the supplied ones, and for the rest the default ones. Fix #762
Add sd_card drivers to some run scripts (fix #757)

Moreover, extend l4android script to run on OMAP4 and Exynos5.
Unify buffer sizes of RX and TX in nic_session

In fact, the sizes were the same the whole time, but by using
the same enum in both cases to instantiate the Packet_stream_tx
and Packet_stream_rx members of the e.g. RPC object, it allows
for more flexible generalization between e.g. source or, sink
objects, when programming event-driven, and implementing generic
handlers for their signals.
Simplify use of custom data-flow signal handlers

This is analogue to the changes done in packet_stream_tx in commit:
cb9b2724de3b9ecba67d0403ff61bd8ba6a3313d
Let the nic_bridge work event driven (fix #749)