SPM: Adjust size of virtual address space per partition

Rather than using a fixed virtual address space size, read all regions
in the resource description of each partition and restrict the virtual
address space size to the one the partition actually needs.

This also allows SPM to take advantage of the extension ARMv8.4-TTST if
the virtual address space size is small enough.

Change-Id: I8646aa95e659136b58b44b040364cdee631f7e82
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>