VICTORY: MAX8893: Handle liblights supplied touchkey brightness.

A variable button brightness can be supplied from liblights on a scale
of 0-255.  Convert those values to previously experimentally determined
voltages for desired brightness levels.

Change-Id: I0c659e49de2ff1ccf00ee0690d4d1228f19611bf
Merge "VICTORY: MAX8893: Handle liblights supplied touchkey brightness." into cm-11.0