input: synaptics_i2c_rmi4: Remove regulator_en property

Regulator will always be required, so use it by default.
Remove unnecessary device tree entry.

This patch is propagated from msm-3.4 kernel.
(commit: 836c0b01ed9531a9d0cfbd6c4c7b5ce7c7d54cbb
input: synaptics_i2c_rmi4: Remove regulator_en property)

Change-Id: If9480e4d6d8b2290eca6f594048948a77ef42d08
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>