mmc: sdhci-of-arasan: Modify clock operations handling

The SDHCI clock operations are platform specific. So it better to define
them separately for particular platform. This will prevent multiple
if..else conditions and will make it easy for user to add their own
clock operations handlers.

Signed-off-by: Manish Narani <manish.narani@xilinx.com>
Link: https://lore.kernel.org/r/1586195015-128992-6-git-send-email-manish.narani@xilinx.com


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