Added BeagleBoard BSP

Coding done in course of GSoC2012.

Commit edited to be brought up-to-date with mainline by
Ben Gras <beng@shrike-systems.com>.
BSP for several Beagle products

Specifically the beagleboard, beagleboard xM, beaglebone, beaglebone black.

More info on these targets: http://www.beagleboard.org/

    This commit forms a basic BSP by combining 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 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.
	  Verified to work when MMU is initially either on or off when
	  RTEMS gets control.

    Thanks for testing, commentary and fixes to Matt Carberry, Brandon
    Matthews, Romain Bornet, AZ technology and others.

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