a5ds: add multicore support

Enable cores 1-3 using psci. On receiving the smc call from kernel,
core 0 will bring the secondary cores out pen and signal an event for
the cores. Currently on switching the cores is enabled i.e. it is not
possible to suspend, switch cores off, etc.

Change-Id: I6087e1d2ec650e1d587fd543efc1b08cbb50ae5f
Signed-off-by: Usama Arif <usama.arif@arm.com>