mmc: host: Add support of 208MHz clock frequency for sdcard

On latest targets, gcc_sdc2_apps clock can support upto 208Mhz.
Update the driver for supporting 208Mhz.

Change-Id: I8c7bb6fffdb8404e0f9ce70883f43adafe864613
Signed-off-by: Ram Prakash Gupta <rampraka@codeaurora.org>