input: ft5x06_ts: add proximity feature support

Focaltech's CTP FT6436 is able to behave like a proximity sensor.
Enable the driver support this new feature.

This patch is propagated from msm-3.10 kernel
(commit: 971ecc03ca03381dde080015c9dabdf45ddec4fc
input: ft5x06_ts: add proximity feature support)
Also cleared the chekpatch warning on 3.18 kernel.
WARNING: void function return statements are not generally useful
+       return;
+}

Change-Id: I7a6ec3a387536c512637b0bd8dab95e7cceca212
Signed-off-by: Mao Li <maol@codeaurora.org>
Signed-off-by: Sudhakar Manapati <smanap@codeaurora.org>