clk: meson: meson8b: add the video decoder clock trees

This adds the four video decoder clock trees.

VDEC_1 is split into two paths on Meson8b and Meson8m2:
- input mux called "vdec_1_sel"
- two dividers ("vdec_1_1_div" and "vdec_1_2_div") and gates ("vdec_1_1"
  and "vdec_1_2")
- and an output mux (probably glitch-free) called "vdec_1"
On Meson8 the VDEC_1 tree is simpler because there's only one path:
- input mux called "vdec_1_sel"
- divider ("vdec_1_1_div") and gate ("vdec_1_1")
- (the gate is used as output directly, there's no mux)

The VDEC_HCODEC and VDEC_2 clocks are simple composite clocks each
consisting of an input mux, divider and a gate.

The VDEC_HEVC clock seems to have two paths similar to the VDEC_1 clock.
However, the register offsets of the second clock path is not known.
Amlogic's 3.10 kernel (which is used as reference) sets
HHI_VDEC2_CLK_CNTL[31] to 1 before changing the VDEC_HEVC clock and back
to 0 afterwards. For now, leave a TODO comment and only add the first
path.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Maxime Jourdan <mjourdan@baylibre.com>
Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190324151423.19063-3-martin.blumenstingl@googlemail.com