Add the GPU clock tree on Meson8, Meson8b and Meson8m2.

The GPU clock tree on Meson8b and Meson8m2 is almost identical to the
one one GXBB:
- there's a glitch-free mux at HHI_MALI_CLK_CNTL[31]
- there are two identical parents for this mux: mali_0 and mali_1, each
  with a gate, divider and mux
- the parents of mali_0_sel and mali_1_sel are identical to GXBB except
  there's no GP0_PLL on these 32-bit SoCs

Meson8 is different because it does not have the glitch-free mux.
Instead if only has the mali_0 clock tree. The parents of mali_0_sel are
identical to the ones on Meson8b and Meson8m2.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20181208171247.22238-4-martin.blumenstingl@googlemail.com