Handle VM availability messages

Add handling for the FF-A VM availability messages to libsp. Currently
this is only a skeleton implementation that calls an empty callback in
the SPs.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: I037f7a67121b7b02ceb1775baf4508abb9455fcd
15 files changed