phy: sun4i-usb: Support secondary clock for HSIC PHY

On the Allwinner A83T SoC, the last USB PHY is an HSIC PHY. It requires
two clocks instead of one.

On all Allwinner SoCs that share the common USB PHY design supported by
the phy-sun4i-usb driver, the first PHY is always tied to OTG, and there
is at most one HSIC PHY, typically the last.

In this patch we take advantage of these known constraints and store an
index in the compatible-string-related config structure describing which
PHY is HSIC, needing the extra hsic_12M clock.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>