clk: Initial support for the SpacemiT K1 clock control units

This change implements the core clknode methods for the SpacemiT K1
clock control units. These methods were used to implement drivers
for

clk: Initial support for the SpacemiT K1 clock control units

This change implements the core clknode methods for the SpacemiT K1
clock control units. These methods were used to implement drivers
for the APMU and PLL CCUs. The initial driver for the APMU CCU
only contains clock definitions for the SDHCI controller for now.

Differential Revision: https://reviews.freebsd.org/D57176
Reviewed by: mmel, mhorne, manu

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