scsi: ufs: add write booster feature support

Write Booster enable: SW will enable the feature
when clocks are scaled up.
Once clocks and gear are scaled up,
SW will set “fWriteBoosterEn” flag
before exiting from ufshcd_devfreq_scale() function.

Write Booster disable: SW will disable the feature,
when clocks are scaled down. Once clocks and gear
are scaled down, SW will clear “fWriteBoosterEn” flag
before exiting from ufshcd_devfreq_scale() function.

Write Booster Buffer flush will be enabled in following cases:
 1. During runtime suspend, driver would query
    bAvailableWriteBoosterBufferSize attribute and enable the
    Write Booster Buffer Flush if less than 30% Write Booster
    Buffer is available.

Write Booster Buffer flush will be disabled in following case:
During runtime suspend, if available buffer size is >30%,
then Write Booster Flush will be stopped by
clearing fWriteBoosterBufferFlushEn flag.

In non-reduction case, during runtime-suspend,
dCurrentWriteBoosterBufferSize attribute would determine
if flush is possible.
If this value is > 0 and availBuf is less
than 30% then flush is needed and vcc needs to be ON.

Change-Id: I89c488a7641697173a296c1ebadc1f4720090cfd
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>