ARM: mxs/tx28: according to the TX28's datasheet D4-D7 are not used for MMC0

The pins are actually used (not in mainline yet):

	D4 -> SSP2_D0
	D5 -> GPIO
	D6 -> GPIO
	D7 -> GPIO for owire

so their pinmapping for SSP0 is wrong.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>