input: synaptics_i2c_rmi4: Reorganize the code

Reorganize the code related to debugfs that allows driver to compile
for different build environments. Remove dead code and also define
dummy functions that are needed when CONFIG_PM is not enabled in defconfig.

Change-Id: I385d194c7463cd06322f1b5124f1dc0ce72fc8a1
Signed-off-by: Himanshu Aggarwal <haggarwa@codeaurora.org>