arch: Added ARMv7R and Cortex-R4 support

Rewrite to merge Cortex-A and Cortex-R code

Change-Id: I4541557980d43d1bba6e8d1bfeb04f536ed25a00
Signed-off-by: Evan Hunter <ehunter@broadcom.com>
Reviewed-on: http://openocd.zylin.com/358
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>