dt-bindings: clk: microchip: Add Microchip PolarFire host binding

Add device tree bindings for the Microchip PolarFire system
clock controller

Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211216140022.16146-2-conor.dooley@microchip.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>