m7-common: fstab updates

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

Change-Id: I2455a37317fff26334e5514b21b5cab7a86656f5
m7: Set primary storage volume

Change-Id: I18d8df8470518fab6859effa19b50f4fa59d00ab
m7-common: Fix deprecated USB syntax

Change-Id: I07fabab95f136e2d056f5b3cb3b6a8ecc467e10f