clk: amlogic: add composite clock helpers

Device composite clocks tend to reproduce the usual sel/div/gate
arrangement.

Add macros to help define simple composite clocks in the system.

The idea is _not_ to replace all instances of mux, div or gate with those
macros. It is rather to use it for recurring and/or simple composite
clocks, reducing controller verbosity where it makes sense. This should
help reviews focus on the tricky parts.

Link: https://lore.kernel.org/r/20250825-meson-clk-cleanup-24-v2-10-0f402f01e117@baylibre.com


Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>