clk: meson: meson8b: use of_clk_hw_register to register the clocks

Switch from clk_hw_register to of_clk_hw_register so we can use
clk_parent_data.fw_name. This will be used to get the "xtal", "ddr_pll"
and possibly others from the .dtb.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>