clk: mediatek: provide common clk init function for infrasys

clk: mediatek: provide common clk init function for infrasys

Provide common clk init function for infrasys that defaults to topckgen
driver if clock-parent is not defined. This is the case for upstream
DTSI that doesn't provide this entry.

This is needed for infracfg driver that will make use of the unified
gates + muxes implementation.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>