doc: add spm and spmd related build options
doc: add spm and spmd related build options

Signed-off-by: Olivier Deprez <a71d93c73db536dc855a04902dabc350f140693d@arm.com>
Change-Id: I93892dbe76611a7a4b852af3272a0e6271ae037b

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware