mmc: meson-gx: support platform interrupt as card detect interrupt

Use a new mmc core feature and support specifying the card detect
gpio interrupt in device tree.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/2bb70611-5dea-1144-51bd-93c46b455392@gmail.com


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