mmc: mmc_spi: parse speed mode options

Since SD and MMC Highspeed modes are also valid for SPI let's parse
them too.

Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20c6efa9a4c7423bbfb9352705c4a53a@hyperstone.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>