MFC r357250, r363926-r363927

r357250 (by ganbold@):
Add USB3 related clock definitions for Rockchip RK3328 SoC.

Reviewed by: manu

r363926:
Add flag for SYSCON-controlled clocks on Rockhip platform

Ethernet clocks on RK3328 are controlled by SYSCON registers, so add
RK_CLK_COMPOSITE_GRF flag to indicate that clock node should access grf
registers instead of CRU's

Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D25918

r363927:
Add clocks for ethernet controllers on RK3328

Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D25918