scsi: ufs: use WQ_HIGHPRI for gating work

Must have WQ_MEM_RECLAIM
``WQ_MEM_RECLAIM``
  All wq which might be used in the memory reclaim paths **MUST**
  have this flag set.  The wq is guaranteed to have at least one
  execution context regardless of memory pressure.

Bug: 158050260
Bug: 155410470
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Link: https://lore.kernel.org/linux-scsi/20200915204532.1672300-3-jaegeuk@kernel.org/T/#u


Change-Id: I65f2608650fa3436503581a60ac539f85273a21e
(cherry picked from commit ceed5e02518f5cedc799f2f37bd30211243a7959)
Signed-off-by: Adam W. Willis <return.of.octobot@gmail.com>