sunxi: Complete mmc pin mux for each supported platform, configured with Kconfig

Sunxi platforms have different possible mmc pin mux setups (except for mmc0),
which are different across platforms.

This lets users configure which is used through the CONFIG_MMC*_PINS Kconfig
options. This is especially relevant when a second (in addition to mmc0) port
is used and CONFIG_MMC_SUNXI_SLOT_EXTRA is enabled.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>