Added BeagleBoard BSP

Coding done in course of GSoC2012. Commented out assertion in
cpukit/libfs/src/imfs/imfs_readlink.c in order to circumvent compilation
error. Needs to be fixed.

Commit edited to be brought up-to-date with mainline by
Ben Gras <beng@shrike-systems.com>.
Basic BSP for BeagleBoard and Beaglebones

This commit combines Claas's work with
	. new clock and irq code and definitions for
	  beagle targets (beagleboard and beaglebones), mostly
	  reused from the Minix codebase, thus making
	  irqs, ticks and non-polled console mode work on the
	  beagleboard too
	. new timer code for ns timing with high timer resolution,
	  24MHz on the AM335X and 13MHz on the DM37XX
	. select the console uart based on target at configure time
	. removing all the lpc32xx-specific macros and code and
	  other unused code and definitions that the beagle bsp
	  was based on
	. re-using some standard functions instead of lpc32xx versions
	. fixed some whitespace problem in preinstall.am
	. fixed some compile warnings
	. configure MMU: set 1MB sections directly in the TTBR,
	  just to show the difference between cacheable RAM and
	  non-cacheable device memory and invalid ranges; this lets us
	  turn on caches and not rely on boot loader MMU configuration.

Signed-Off-By: Ben Gras <beng@shrike-systems.com>