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
Merge remote-tracking branch 'upstream/cm-11.0' into cm-11.0