dt-bindings: mmc: Add new compatible string for sm8250 target

Add new compatible string for sm8250 target.

Signed-off-by: Sarthak Garg <sartgarg@codeaurora.org>
Link: https://lore.kernel.org/r/1590139950-7288-2-git-send-email-sartgarg@codeaurora.org


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