platform: qpnp-power-on: Add boot mode module parameter

Warm boot runs may not last until the point where pon driver
has had a chance to read the warm boot registers. We need a way
to identify a warm boot in the crashes and hence we expect
bootloader to set this in kernel command line.
We may use this parameter later in the driver for
debug/verficiation purposes.

Change-Id: I7a462cc5660384e345b07553b7ae4cccdee56608
Signed-off-by: Hanumant Singh <hanumant@codeaurora.org>