arm/dt: msm8610: Modify LPM levels

As retention on core and L2 GDHS is not supported, remove the low
power level. Add L2 retention as low power level as a substitue
for L2 GDHS. Also add a property to detect irqs and gpios at mpm
when xo is off.

Change-Id: Ib911bad9405481e7516c168b1f8bb3584075d8c7
Signed-off-by: Priyanka Mathur <pmathur@codeaurora.org>