nRF51822: Add workaround for PAN-16 where not all RAM blocks reliably enabled on...

nRF51822: Add workaround for PAN-16 where not all RAM blocks reliably enabled on reset

According to Nordic Semiconductor Product Anomaly Notice (document
NRF51822-PAN), item 16, some revisions of nRF51822 sometimes reset
without all RAM blocks enabled. This was noted on NRF51822-QFAA rev
CA/C0, only 8KiB of memory was accessible.

This patch turns on all RAM following a debugger induced reset
(matches specified behaviour.)

Change-Id: I4f8be4ec3d1271da7fe5bc9a084fdcb2968535bb
Signed-off-by: Angus Gratton <gus@projectgus.com>
Reviewed-on: http://openocd.zylin.com/2202
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>