mtd: mxc_nand: reorder part_probes to let cmdline override other sources

The cmdline is the easiest to change source of information. Thus
let it take precedence over 'RedBoot' and 'ofpart'. This makes the
mxc_nand driver to be in sync with all other NAND drivers that support
'cmdlinepart' partition parsing.

Also change 'const char *' to 'const char const *' as advised by checkpatch.pl

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>