vs920: updates for 11.0

 * Update permissions for /firmware mount
 * Add mount for /modem
 * Update sdcard entry
 * Remove unused /drm mount

Change-Id: If460ba17adaf672e75bb3fc6c612165a8cf0ebb3
vs920: remove TARGET_DEVICE override

This lets the recovery build with the proper device tag

Change-Id: I2c6fe999012854cb39b577d85d3a87c63e9e4133