ARM/mmc: Convert old mmci-omap to GPIO descriptors

A recent change to the OMAP driver making it use a dynamic GPIO
base created problems with some old OMAP1 board files, among
them Nokia 770, SX1 and also the OMAP2 Nokia n8x0.

Fix up all instances of GPIOs being used for the MMC driver
by pushing the handling of power, slot selection and MMC
"cover" into the driver as optional GPIOs.

This is maybe not the most perfect solution as the MMC
framework have some central handlers for some of the
stuff, but it at least makes the situtation better and
solves the immediate issue.

Fixes: 92bf78b3 ("gpio: omap: use dynamic allocation of base")
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>