scsi: ufs: add manual_gc in sysfs

This patch adds manual_gc control via sysfs entries.

 > cat /sys/devices/platform/soc/1d84000.ufshc/manual_gc
on
 > echo 1 > /sys/devices/platform/soc/1d84000.ufshc/manual_gc

Bug: 63264275
Bug: 68721792
Change-Id: I4e778f716eed3e5a076e5d831a3b653ba8cd8458
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
4 files changed