clk: thead: Add clock support for VO subsystem in T-HEAD TH1520 SoC

The T-Head TH1520 SoC integrates a variety of clocks for its subsystems,
including the Application Processor (AP) and the Video Output (VO) [1].
Up until now, the T-Head clock driver only supported AP clocks.

Extend the driver to provide clock functionality for the VO subsystem.
At this stage, the focus is on implementing the VO clock gates, as these
are currently the most relevant and required components for enabling and
disabling the VO subsystem functionality.  Future enhancements may
introduce additional VO-related clocks as necessary.

Link: https://openbeagle.org/beaglev-ahead/beaglev-ahead/-/blob/main/docs/TH1520%20System%20User%20Manual.pdf

 [1]

Reviewed-by: Drew Fustini <drew@pdp7.com>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Signed-off-by: Drew Fustini <drew@pdp7.com>