sunxi-mmc: introduce new MMC_SUNXI_HAS_MODE_SWITCH option

Allwinner A64 has new mode but doesn't have a mode switch in CCM,
and CCM_MMC_CTRL_MODE_SEL_NEW is not defined, so compilation fails
if MMC_SUNXI_HAS_NEW_MODE is enabled

Introduce new MMC_SUNXI_HAS_MODE_SWITCH option to be able to ifdef usage
of CCM_MMC_CTRL_MODE_SEL_NEW

Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
[jagan: update commit message]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com> # Amarula A64-Relic