scsi: ufs-qcom: add debug prints for test bus

Adds support for configuring and reading the test bus and debug
registers. The configuration is controlled by debugfs. Reading can
be triggered either by debugfs or by the kernel code.

Change-Id: I943e3c1b1e383a91a8abbb8dab9714434c56b6f5
Signed-off-by: Dov Levenglick <dovl@codeaurora.org>