clk: mediatek: mt7981: drop 1/1 spurious factor

Now that we can have advanced parent handling for mux, we can drop
spurious infracfg 1/1 factor. This is in preparation to make the clk
ID match the ID in upstream include for mt7981.

Drop the factor entry from mt7981-clk.h and reference to them in
mt7981.dtsi. Muxes and gates are updated to reference the topckgen clk
following how it's done in upstream kernel linux. Add relevant clk type
flag in clk_tree for infracfg and topckgen.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>