drivers: staging: rename synaptics_i2c_rmi4 to avoid confusion

Synaptics driver in staging directory has the same file
name as the in-use synaptics driver in touchscreen directory.
Rename so that in search it is obvious they are two different
files and both are not enabled.

Change-Id: I53c81fbeb97b95f458dfbb60744cb95aa64c6275
Signed-off-by: Amy Maloche <amaloche@codeaurora.org>