Fix normal memory bakery lock implementation

Fix normal memory bakery lock implementation

This patch fixes an issue in the normal memory bakery lock
implementation. During assertion of lock status, there is a possibility
that the assertion could fail. This is because the previous update done
to the lock status by the owning CPU when not participating in cache
coherency could result in stale data in the cache due to cache maintenance
operations not propagating to all the caches. This patch fixes this issue
by doing an extra read cache maintenance operation prior to the assertion.

Fixes ARM-software/tf-issues#402

Change-Id: I0f38a7c52476a4f58e17ebe0141d256d198be88d
Signed-off-by: Soby Mathew <soby.mathew@arm.com>