firmware: psci: setup OSI mode at init

Let's switch to OSI mode for QCOM platforms if setting the OSI mode is
supported. We should do this only if the lpm-levels driver is used.
Other VMs using the same kernel but defaulting to ARM cpuidle drivers,
will default to platform coordinated.

Change-Id: I69245bf33361970f37ea2006d669368e30e2ec9d
Signed-off-by: Lina Iyer <ilina@codeaurora.org>