fix(xilinx): register for idle callback

Currently, only Linux registering for getting idle callback during
subsystem restart or force power down. Because of that if Linux boot
hang or someone wants to do subsystem restart before Linux boot then
it's not working. So, register for idle callback in TF-A to get idle
callback during subsystem restart or force power down to do ARM
specific steps for proper power down of core.

Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti@amd.com>
Change-Id: If7c01f79be6958678243be844bcfdc50d59b0fb8
1 file changed