clk: microchip: mpfs: support new syscon based devicetree configuration

clk: microchip: mpfs: support new syscon based devicetree configuration

Why get a devicetree description wrong once when you can get it wrong
twice? The original mistake, which the driver supports was failing to
describe the main PLL that the "cfg" and "periph" clocks parented by.
The second mistake was describing the "cfg" and "periph" clocks a
reg region within the clock controller, rather as two registers within
a syscon region that also contains pinctrl, interrupt muxing controls
and other functions.

Make up for lost time and describe these regions as they should have
been originally, preserving support for the existing two configurations
for the sake of existing systems with firmware-provided devicetrees.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>