clk: meson: axg: migrate to the new parent description method

This clock controller use the string comparison method to describe parent
relation between the clocks, which is not optimized.

Migrate to the new way by using .parent_hws where possible (ie. when
all clocks are local to the controller) and use .parent_data otherwise.
Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>