mmc: omap_mmc: Remove invert references

With DM_GPIO and DM_MMC translating GPIO_ACTIVE_LOW, any boards
using the 'cd-invert' option will no longer need to do this.  This
patch removes the support for 'invert' from the MMC driver.

Signed-off-by: Adam Ford <aford173@gmail.com>
[trini: Fix warning over when !DM_GPIO]
Signed-off-by: Tom Rini <trini@konsulko.com>