[MTD] LPDDR PFOW definition

LPDDR chips use PFOW window for sending commands, reading status and
capabilites requesting.
This pfow.h - contains definitions for PFOW window fileds, possible commands,
error flags and some common macro function to avoid code duplications.

Signed-off-by: Alexey Korolev <akorolev@infradead.org>
Acked-by: Jared Hulbert <jaredeh@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>