d855: 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

rootdir/etc/fstab.g3

@@ -7,8 +7,8 @@
 
 #<src>                                              <mnt_point>     <type>  <mnt_flags and options>                                             <fs_mgr_flags>
 /dev/block/platform/msm_sdcc.1/by-name/system       /system         ext4    ro,barrier=1,noatime                                                wait,recoveryonly
-/dev/block/platform/msm_sdcc.1/by-name/userdata     /data           f2fs    rw,nosuid,nodev,noatime,nodiratime,inline_xattr                     wait,check,formattable,encryptable=/dev/block/platform/msm_sdcc.1/by-name/encrypt
-/dev/block/platform/msm_sdcc.1/by-name/userdata     /data           ext4    noatime,nosuid,nodev,barrier=1,noatime,noauto_da_alloc,errors=continue,journal_async_commit wait,check,formattable,encryptable=/dev/block/platform/msm_sdcc.1/by-name/encrypt
+/dev/block/platform/msm_sdcc.1/by-name/userdata     /data           f2fs    rw,nosuid,nodev,noatime,nodiratime,inline_xattr                     wait,check,formattable,encryptable=/dev/block/platform/msm_sdcc.1/by-name/encrypt,reservedsize=128M
+/dev/block/platform/msm_sdcc.1/by-name/userdata     /data           ext4    noatime,nosuid,nodev,barrier=1,noatime,noauto_da_alloc,errors=continue,journal_async_commit wait,check,formattable,encryptable=/dev/block/platform/msm_sdcc.1/by-name/encrypt,reservedsize=128M
 /dev/block/platform/msm_sdcc.1/by-name/cache        /cache          f2fs    rw,nosuid,nodev,noatime,nodiratime,inline_xattr                     wait,check,formattable
 /dev/block/platform/msm_sdcc.1/by-name/cache        /cache          ext4    noatime,nosuid,nodev,barrier=1,data=ordered,journal_async_commit    wait,check,formattable
 /dev/block/platform/msm_sdcc.1/by-name/persist      /persist        ext4    nosuid,nodev,barrier=1,data=ordered,nodelalloc,nomblk_io_submit,errors=panic wait,notrim