xlat: Introduce API to change memory attributes of a region

xlat: Introduce API to change memory attributes of a region

This patch introduces a new API in the translation tables library
(v2), that allows to change the memory attributes of a memory
region. It may be used to change its execution permissions and
data access permissions.

As a prerequisite, the memory must be already mapped. Moreover, it
must be mapped at the finest granularity (currently 4 KB).

Change-Id: I242a8c6f0f3ef2b0a81a61e28706540462faca3c
Co-authored-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Co-authored-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>