Fix incorrect pointer conversion in SMC_UUID_RET()

Fix incorrect pointer conversion in SMC_UUID_RET()

Casting a pointer to a struct uuid into a pointer to uint32_t may
result in a pointer that is not correctly aligned, which constitutes
an undefined behaviour. In the case of TF, this also generates a data
abort because alignment fault checking is enabled (through the SCTLR.A
bit).

This patch modifies the SMC_UUID_RET() macro to read the uuid
structure without any pointer aliasing. A helper function then
combines every set of 4 bytes into a 32-bit value suitable to be
returned through the x0-x3 registers.

This fixes a violation of MISRA rule 11.3.

Change-Id: I53ee73bb4cb332f4d8286055ceceb6f347caa080
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>