[MTD] [NAND] at91_nand.c: CMDLINE_PARTS support

This patch allows you to specify at91_nand partitions on the
kernel command line using the mtdparts variable, if
CONFIG_MTD_CMDLINE_PARTS is set.

Signed-off-by: Frank Mandarino <fmandarino@endrelia.com>
Signed-off-by: Andrew Victor <andrew@sanpeople.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>