With the new clk parenting code and CLK_FIXED_FACTOR_{HW,FW_NAME}
macros, we can reference parents locally via pointers to struct clk_hw
or DT clock-names.

Convert existing CLK_FIXED_FACTOR definitions to either the _HW or
_FW_NAME variant based on whether the parent clock is internal or
external to the CCU.

A forward declaration for struct clk_fixed_factor pll_periph0_4x_clk
is added as the definitions of the fixed factor clocks appear much later
in the file. The position of fixed factor clock definitions will be
moved for all drivers at a later time, before the conversion of all
other clock types.
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>