Enable UMS mounting of storage drives

Change-Id: Iaba2c1579936bfdcf3e707cdaf9b30f6696fd10c
Specify backlight brightness path

* Allows TWRP to set and store a backlight brightness via Settings
* Allows TWRP to blank and restore display via brightness values

Change-Id: I9e9dbca0fb5630ad038034c04152a52d38fbf493