riscv: dts: microchip: icicle: Add GPIO controlled LEDs

Add the 4 GPIO controlled LEDs to the Microchip PolarFire-SoC Icicle
Kit device tree. The schematic doesn't specify any special function
for the LEDs, so they're added here without any default triggers and
named led1, led2, led3 and led4 just like in the schematic.

Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>