platform: stm32u5xx: Add missing stm32u5a5xx.h

The file stm32u5a5xx.h is part of the stm hal to enable support to
stm32u5a5xx mcu. For some unknown reason this file still missing
and code do not compile. Add the missing file to fully support out
of tree tf-m to this plaform.

Change-Id: Ib1971a9231af90b4877d45801afc5accea2484cb
Signed-off-by: BUDKE Gerson Fernando <[email protected]>
Signed-off-by: Ahmad EL JOUAID <[email protected]>

(cherry picked from commit 3376880113cb75ce82d4fd05a02775ff1e9ee6b9)

Author: nandojve