Userspace may want to manually control when the data should go into
WriteBooster buffer. The control happens via "wb_on" node, but presently,
there is no simple way to check if WriteBooster is supported and
enabled.

Expose the Write Booster and Clock Scaling capabilities to be able to
determine if the Write Booster is available and if its manual control is
blocked by Clock Scaling mechanism.

Link: https://lore.kernel.org/r/20220829081845.v8.1.Ibf9efc9be50783eeee55befa2270b7d38552354c@changeidReviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Daniil Lunev <dlunev@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>