Reserve 128MB for critical system components.

We recently created a new GID that can be granted to critical system
processes, so that the system is usable enough for the user to free
up disk space used by abusive apps.

128MB ought to be enough for anybody.

Test: builds, boots
Bug: 62024591
Change-Id: I412ed9b0a885668ebe4c6c677a3bd0cd7f44080b

fstab.common

@@ -8,7 +8,7 @@
 #<src>                                                  <mnt_point>         <type>  <mnt_flags and options>     <fs_mgr_flags>
 /dev/block/platform/soc/624000.ufshc/by-name/system     /                   ext4    ro,barrier=1                wait,slotselect,verify
 /dev/block/platform/soc/624000.ufshc/by-name/modem      /firmware/radio     vfat    ro,shortname=lower,uid=1000,gid=0,dmask=227,fmask=337,context=u:object_r:firmware_file:s0   wait,slotselect
-/dev/block/platform/soc/624000.ufshc/by-name/userdata   /data               ext4    errors=panic,noatime,nosuid,nodev,barrier=1,noauto_da_alloc  latemount,wait,check,formattable,fileencryption=ice,quota
+/dev/block/platform/soc/624000.ufshc/by-name/userdata   /data               ext4    errors=panic,noatime,nosuid,nodev,barrier=1,noauto_da_alloc  latemount,wait,check,formattable,fileencryption=ice,quota,reservedsize=128M
 /dev/block/zram0                                        none                swap    defaults                    zramsize=536870912,max_comp_streams=4
 /dev/block/platform/soc/624000.ufshc/by-name/misc       /misc               emmc    defaults                    defaults
 /devices/*/xhci-hcd.0.auto/usb*                         auto                vfat    defaults                    voldmanaged=usb:auto