clk: mediatek: Add MT8196 pextpsys clock support

clk: mediatek: Add MT8196 pextpsys clock support

Add support for the MT8196 pextpsys clock controller, which provides
clock gate control for PCIe.

Co-developed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org> # CLK_OPS_PARENT_ENABLE removal
Signed-off-by: Laura Nao <laura.nao@collabora.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>