cortex-m: Clean up MPU logic

Add error checking for failures and use IS_ENABLED combined with helper
functions for readability.

BRANCH=none
BUG=b:155229277, b:156501835
TEST=Compile and flash "rollback" test on dragonclaw with region 0
     On console: "runtest"
     => Reboots with "Data access violation, mfar = 8020000"
	=> PASS
TEST=Compile and flash "rollback" test on dragonclaw with region 1
     On console: "runtest"
     => Memory is successfully read
        => FAIL
TEST=Compile and flash "rollback" test on dragontalon with region 0
     On console: "runtest"
     => Reboots with "Data access violation, mfar = 80c0000"
        => PASS
TEST=Compile and flash "rollback" on dragontalon with region 1
     On console: "runtest"
     => Reboots with "Data access violation, mfar = 80e0000"
        => PASS

Signed-off-by: Tom Hughes <tomhughes@chromium.org>
Change-Id: I0f8d149c8c5c568241457a6779079c65eb38ce32
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2200199
Commit-Queue: Jett Rink <jettrink@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>

0 files changed, 0 insertions, 0 deletions