[PORT FROM R2] hsu: port recent fix from R2

[PORT FROM R2] hsu: port recent fix from R2

BZ: 21502

The fix hsu: turn off RX dma before runtime suspend was merged in R2
need port it to R3.(BZ 18936)

Also include a fix for holding tty ref during rx dma handling.(BZ 21234)

Change-Id: I88647c9fb50d7f8c3056b70d37b5a8fe972ec645
Signed-off-by: Alek Du <alek.du@intel.com>
Reviewed-on: http://android.intel.com:8080/33119
Reviewed-by: Cai, Stanley W <stanley.w.cai@intel.com>
Tested-by: Wang, Zhifeng <zhifeng.wang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>