The i.MX7 has the same GPMI controller as i.MX6 and is covered by the MXS
driver. Tell Kconfig that we can use this driver on the MX7 platform (the MXS
driver already has the few i.MX7-specific changes needed for basic operation
and the board itself sets the pinmux correctly).

Tested on i.MX7D with the Sabre board and a NAND Flash soldered to U12.

Signed-off-by: Andrey Yurovsky <yurovsky@gmail.com>