clk_div: Add a div lookup table

[manu]

Summary

Some clocks on SoC have a diff between the value written in the register and the real divider. Add a table that where we can lookup the real value of the divider.
Allwinner have those and since I'm pretty sure that it's kinda standard make it generic.

Test Plan

Tested on Allwinner H3 which have a div table for APB1.

[mmel]

See a small inline comment.
Also, please use full diff (-U9999999) next time. The full context is exceptionally easier for review.

sys/dev/extres/clk/clk_div.c

137

Panic (or report error) here if divider value is not found in table. Although we have check for divider == 0 in clknode_div_recalc(), it's better to report problem immediately...

[manu]

sys/dev/extres/clk/clk_div.c

137

I didn't put a warn because of the check in recalc but I guess a panic in init would be better