clk: mediatek: clk-mt8195-mfg: Reparent mfg_bg3d and propagate rate changes

clk: mediatek: clk-mt8195-mfg: Reparent mfg_bg3d and propagate rate changes

The MFG_BG3D is a gate to enable/disable clock output to the GPU,
but the actual output is decided by multiple muxes; in particular:
mfg_ck_fast_ref muxes between "slow" (top_mfg_core_tmp) and
"fast" (MFGPLL) clock, while top_mfg_core_tmp muxes between the
26MHz clock and various system PLLs.

The clock gate comes after all the muxes, so its parent is
mfg_ck_fast_reg, not top_mfg_core_tmp.
Reparent MFG_BG3D to the latter to match the hardware and add the
CLK_SET_RATE_PARENT flag to it: this way we ensure propagating
rate changes that are requested on MFG_BG3D along its entire clock
tree.

Fixes: 35016f10c0e5 ("clk: mediatek: Add MT8195 mfgcfg clock support")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220927101128.44758-6-angelogioacchino.delregno@collabora.com
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>