scsi: ufs: rework unit test infrastructure

Upgrade the APIs used.
Encapsulate test ops (read/write/open functions) and dentry creation
in macros.
Fix naming collisions with mmc tests.

Change-Id: I5c48b369beaf902f8187ced9d884a2149a8644f0
Signed-off-by: Dolev Raviv <draviv@codeaurora.org>