[HACK] css_pm: support warm reboot on FVP platforms

In FVP platforms, during a warm reboot, it is observed that PPI
interrupt 26 is waking up the AP core in dynamic OFF even before SCP
put the cores into static OFF. This is identified as bug in FVP, and
keeping this patch as a workaround to overcome the issue.

It is recommended to revert this patch if tests are done on RTL/FPGA
platforms.

Change-Id: I13888b98a7f11d1246de576e1be813fcb0df7570
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>