scsi: ufs: Enable WriteBooster

The write performance of TLC NAND is considerably lower than SLC NAND.
Using SLC NAND as a WriteBooster Buffer enables the write request to be
processed with lower latency and improves the overall write
performance.

Adds support for shared-buffer mode WriteBooster.

WriteBooster enable:
SW enables it when clocks are scaled up, thus it's
enabled only in high load conditions.

WriteBooster disable:
SW will disable the feature, when clocks are scaled
down. Thus writes would go as normal writes.

To keep the endurance of the WriteBooster Buffer at a maximum, this
load-based toggling is adopted.

Change-Id: I55a348f17e2d29b46ed9b29960254937c146f147
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>