mtd: nand: gpmi: fix function annotations

A lot of functions have been marked __devinit, but they shouldn't, because they
are needed for bbt_scan. While I believe the whole MX23 handling should be done
entirely different, I am missing the resources to fix it. So, let's have at least
the annotations correct.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>