mmc: sdhci-iproc: Use defines instead of magic numbers

The capabilities in iproc platform data are magic numbers. So
replace them with the proper capability defines to make it
readable.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>