ubifs: Enable journal replay during mount

Enable ubifs_replay_journal during mount_ubifs, which was
disabled before.

This commit fix an issue with unrecoverable ubifs volumes
after power cut.

Therefor the gc.c is imported now from 1860e37 Linux 3.15

hs: added SPDX-License-Identifier for fs/ubifs/gc.c

Signed-off-by: Anton Habegger <anton.habegger@gmail.com>
diff --git a/fs/ubifs/Makefile b/fs/ubifs/Makefile
index 8c8c6ac..5efb349 100644
--- a/fs/ubifs/Makefile
+++ b/fs/ubifs/Makefile
@@ -12,4 +12,4 @@
 obj-y := ubifs.o io.o super.o sb.o master.o lpt.o
 obj-y += lpt_commit.o scan.o lprops.o
 obj-y += tnc.o tnc_misc.o debug.o crc16.o budget.o
-obj-y += log.o orphan.o recovery.o replay.o
+obj-y += log.o orphan.o recovery.o replay.o gc.o