clocks: move pllv2 to the drivers/clk directory

Here it shall live until the end-times.

clk-imx now does all the fancy OF init meaning clk-imx-pllv2.c is pretty
much standalone again and we could bring back the hacky non-DT clock inits
without trampling all over each other.

It also means we are close enough to safely and/or subtley remove DT clocks
from clk-imx51-imx53.c on a one-by-one basis and/or move that entire
clock array horseshit into a clk-imx5-ccm driver in the same place for example.

This is only really possible as the only users of the pllv2 code are MX5,
and we ditched all the dependencies on that clock init already in this
experimental tree, but even upstream this would be low-impact on everyone
else's clock handling. Moving the other stuff (clk-gate2 etc.) may be a
little more of a challenge but not truly difficult (as long as they get
compiled where needed in it is ALL fine).