hw: cfi flash: Handle errors in memory transitions

Handle failures in creating the memory maps and back in
transitioning the CFI flash. e.g., with MTE enabled, CFI
flash emulation breaks with the map operation, silently.
And we later hit unhandled aborts in the guest.

To avoid such issues, let us make sure we catch the error
and handle it right at source.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>