msm: rpc_server_handset: Add support to ignore END key

Legacy targets (7201, 7627, 7630..) using this driver use
a key to report both END(short press) and POWER(long press).
Recent targets that use this driver (QRD7x27a platform)
needs the same key only for power. END functionality is to be
supported from UI interface. Sending both END and POWER cause
problems in these targets. So add support to ignore end key for
such platforms.

Change-Id: I636ac3eae5cd60041121e1d0ab0b1f169743c76b
Signed-off-by: Mohan Pallaka <mpallaka@codeaurora.org>