mmc: pxa: Remove the old non-generic PXA MMC driver

This driver is no longer used and it's remaining users were converted
to the new generic PXA MMC driver. Thus, remove this driver.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andy Fleming <afleming@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>