Revert "irq-gic-v3: Disable group pending interrupts before hotplug"

This reverts 'commit 635ad4a3 ("irq-gic-v3: Disable group
pending interrupts before hotplug")'

Commit "635ad4a3" is configuring the "ICC_GRPEN1_EL1" to ZERO
when the CPU is hotplugged. On stress hotplug test scenarios it
is observed that sometimes CPU is waking up from hotplug without
any cpu_on notification from HLOS. After debug it is found that
CPU is waking up due to SGI0 (reschedule) interrupt was pending
at QGIC and causes the CPU wakeup. After reverting commit
"635ad4a3", if there is an SGI pending it will handled by
CPU before it is enter into HOTPLUG state.

Change-Id: I5c133dc3606176eb23a04a345b3adbb32ce1f958
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>