clk: sunxi: Implement MMC phase control

HdG: add header exporting clk_sunxi_mmc_phase_control

Signed-off-by: Emilio López <emilio@elopez.com.ar>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>