StandaloneMmPkg: parse SP manifest and populate new boot information

This patch discovers the SP manifest in DT format passed by the SPMC. It then
parses it to obtain the boot information required to initialise the SP.

Signed-off-by: Achin Gupta <achin.gupta@arm.com>
Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: I04236799c92817e887ff3f80be2e2635101006c3