clk: meson-gxbb: Add MALI clocks

The Mali is clocked by two identical clock paths behind a glitch free mux
to safely change frequency while running.

The two "mali_0" and "mali_1" clocks are composed of a mux, divider and gate.
Expose these two clocks trees using generic clocks.
Finally the glitch free mux is added as "mali" clock.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/1490177935-9646-3-git-send-email-narmstrong@baylibre.com