test(realm): add plane PSI interface

Add Plane service routine interface.
Aux plane can communicate with primary plane using PSI
PSI uses hvc conduit from aux plane.
Add initial printf support for planes

Signed-off-by: Shruti Gupta <shruti.gupta@arm.com>
Change-Id: I484cbd32791970c6e22c5d63e13b43807f4f3c06
16 files changed