lpm-levels: Do not disable non-sec interrupts in suspend

When the system suspend is happening, last core disables
the non-sec interrupts at QGIC by setting the GRPEN1_EL1_NS
to ZERO. This makes core not seen any non-sec interrupts
and would result into system do not wake up from any of
interrupts. Do not touch GRPEN1_EL1_NS register while
system is going into suspend.

Change-Id: I7d6c5047fb4743df187fe49fba18b64db3179bc9
Signed-off-by: Murali Nalajala <mnalajal@codeaurora.org>