mtd: gpmi: do not include the mxs.h

The mxs.h does not exit in the mx6q.
So rewrite the __mxs_clrl()/__mxs_setl() and remove the mxs.h.

Signed-off-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>