clk: meson: meson8b: add the VPU clock trees

The VPU clock tree is slightly different on all three supported SoCs:

Meson8 only has an input mux (which chooses between "fclk_div4",
"fclk_div3", "fclk_div5" and "fclk_div7"), a divider and a gate.

Meson8b has two VPU clock trees, each with an input mux (using the same
parents as the input mux on Meson8), divider and a gates. The final VPU
clock is a glitch-free mux which chooses between VPU_1 and VPU_2.

Meson8m2 uses a similar clock tree as Meson8b but the last input clock
is different: instead of using "fclk_div7" as input Meson8m2 uses
"gp_pll". This was probably done in hardware to improve the accuracy of
the clock because fclk_div7 gives us 2550MHz / 7 = 364.286MHz while
GP_PLL can achieve 364.0MHz.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190324151104.18397-5-martin.blumenstingl@googlemail.com