clk: meson: add the gxl hdmi pll

The hdmi pll used in the gxl family is actually different from the gxbb
one. The register layout is completely different, which explain why the
hdmi pll rate has always been rubbish on the gxl family.

Adding the correct register field is the first part of the fix to get a
correct rate out the hdmi pll

Fixes: 0d48fc55 ("clk: meson-gxbb: Add GXL/GXM GP0 Variant")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>