riscv: dts: microchip: add missing compatibles for clint and plic

The Microchip Icicle kit uses SiFive E51 and U54 cores, so it looks that
also Core Local Interruptor and Platform-Level Interrupt Controller are
coming from SiFive.  Add proper compatibles to silence dtbs_check
warnings:

  clint@2000000: compatible:0: 'sifive,clint0' is not one of ['sifive,fu540-c000-clint', 'canaan,k210-clint']
  interrupt-controller@c000000: compatible:0: 'sifive,plic-1.0.0' is not one of ['sifive,fu540-c000-plic', 'canaan,k210-plic']

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20210920130412.145231-1-krzysztof.kozlowski@canonical.com