semihosting armv7a: Add support for ARMv7-A

semihosting armv7a: Add support for ARMv7-A

Add semihosting support for ARMv7-A based processors.

Tested with custom Vybrid VF610 based board
and Pandaboard ES (Rev. B1) board (Cortex-A9).

Change-Id: I6b896a61c1c6a1c5dcf89de834486f82dd6c80a2
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Tsung-Han Lin <tsunghan.tw@gmail.com>
Reviewed-on: http://openocd.zylin.com/2908
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Tested-by: jenkins