iomux-mx25.h slew rate adjusted for LCD __LD pins

For some reason (sadly i don't identifying the patch right now)
two LCD data lines configured PAD_CTL_SRE_SLOW (wrong slew rate)
since Kernel 3.1. MX25_PAD_GPIO_E__LD16 and MX25_PAD_GPIO_F__LD17
This results in an fauly behaviour and strange color effects.

To ensure that all LCD data pins configured with the proper slew rate,
this patch changes to IOMUX define of all LCD __LDxx pins to PAD_CTL_SRE_FAST.

This problem may affect other mx25 platforms like mx25pdk. Sadly i can't test
it. Of course this problem shouldn't occur when you done your LCD muxing
correctly in the bootloader.

Best regards,
Torsten

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>