input: synaptics_i2c_rmi4: Add low power mode

Enable regulators to go into low power mode when
device enters suspend, to save power.  In resume,
return regulators to full power.

This patch is propagated from msm-3.4 kernel.
(commit: 827e8b0e09bead9a9d3cb26b2ffd4df0e5cdb16b
input: synaptics_i2c_rmi4: Add low power mode)

Change-Id: I6f5a6d398732b2e23aeba81b3569ae2c081f31e5
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>