boards/msba2-based: move shared code to common/msba2

boards/avsextrem/Makefile

boards/avsextrem/Makefile.dep

boards/avsextrem/Makefile.include

boards/common/msba2/Makefile

boards/common/msba2/Makefile.dep

boards/common/msba2/Makefile.include

boards/common/msba2/board_common_init.c

boards/common/msba2/drivers/Makefile

boards/common/msba2/drivers/include/sht11-board.h

boards/common/msba2/include/msba2_common.h

boards/common/msba2/tools/CHANGES

boards/common/msba2/tools/COPYING

boards/common/msba2/tools/Makefile

boards/common/msba2/tools/README.txt

boards/common/msba2/tools/armtools.txt

boards/common/msba2/tools/flash.cmd

boards/common/msba2/tools/flashutil.sh

boards/common/msba2/tools/mkbootc

boards/common/msba2/tools/mkstaticlist

boards/common/msba2/tools/obj/.gitignore