SPM: build OP-TEE as an S-EL1 Secure Partition ...

Provide manifest and build options to boot OP-TEE as a
guest S-EL1 Secure Partition on top of Hafnium in S-EL2.

Increase ARM_SP_MAX_SIZE to cope with OP-TEE debug build image.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: Idd2686fa689a78fe2d05ed92b1d23c65e2edd4cb