mtd: nand: gpmi-nand: Remove wrong Kconfig help text

The GPMI nand Kconfig help texts mentions that the GPMI nand driver
might conflict with SD cards. The only conflict there might really
be is that both controllers use the same pins, but this is resolved
by the pincontroller setup in the device tree. In any way the GPMI
driver can safely be enabled, the text is just wrong. Remove it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Han Xu <han.xu@nxp.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>