m7-common: fstab updates

fstab.qcom.gsm --> fstab.qcom: vzw also uses .gsm fstab
gsm + vzw: enable barriers
spr: set /system ro on mount

Conflicts:
	rootdir/etc/fstab.qcom.spr

Change-Id: I2455a37317fff26334e5514b21b5cab7a86656f5
m7-common: use by-name paths for partitions in fstab

Conflicts:
	rootdir/etc/fstab.qcom.spr

Change-Id: I0575efd29d31359ca9243e8967e919b509776575
m7-common: disable secure discard for ext4 wipes

Users are reporting really long wipe times in recovery on ext4
partitions.

Change-Id: I92dc84b2912684745521176bdb3d61d83e3d4130
Fix USB tether

Conflicts:
	overlay/frameworks/base/core/res/res/values/config.xml

Change-Id: I10b19d4fb86fe477655af369726bc26ba301c0f4