omap1: mmc: Add platform init for omap7xx

The MMC mux pins normally used by omap chips in devices.c
are different from what is needed by omap7xx chips.  This
change adds a conditional around the mux setup code to
enable the correct mux pins.

The omap730 and omap850 both use a different clock for the "fck"
clock of the MMC interface than other omap processors based on the
SOFT_REQ_REG, pin 12.  The "ick" clock is the same as that used
by other omap processors.

* Added the missing clock definition as mmc3_ck to clock.h
* Added the clock definition to omap_clks in clock.c
* Added CK_7XX to the mmci-omap.0 "ick" clock already in clock.c

With these changes, it is now possible to initialize and use MMC
cards with omap730 and omap850 devices.

Signed-off-by: Cory Maccarrone <darkstar6262@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>