arm: cmsis: Convert _ClearFaults to use direct CMSIS register access

The previous code incorrectly used the value 0xfe to clear the mem and
bus faults. It attempted to handle the address register valid bits
separately, but reversed the bit order.

Jira: ZEP-1568

Change-Id: I240d072610af9979ca93c0081ed862df08929372
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
Signed-off-by: Maureen Helm <maureen.helm@nxp.com>