clk: at91: allow configuring peripheral PCR layout

The PCR register actually changed layout for each SoC. By chance, this
didn't have impact on sama5d[2-4] support but since sama5d3, PID is seven
bits wide and sama5d4 and sama5d2 don't have DIV.

For the DT backward compatibility, keep the layout as is.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>