clk: meson: add peripheral gate macro

clk: meson: add peripheral gate macro

There are a series of peripheral and system gate clocks that fan out
from the clk81 signal. Add a helper macro to statically initialize these
gate clocks.

Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>