MFC r355173, r355190-r355191

r355173 by mmel:
Add driver for temperature sensors found in RK32898, RK3328 and RK3399 SoC's.

Reviewed by: manu
Differential Revision: https://reviews.freebsd.org/D22442

r355190:
arm64: rockchip: tsadc: Do not free the sysctl context is it wasn't created

X-MFC-With: r355173

r355191:
arm64: rockchip: rk3328: Add TSADC clocks

Add the clocks so we can use the rk_tsadc driver to monitor
the cpu temperature.