riscv: dts: microchip: mpfs: Drop empty chosen node

It does not make sense to have an (empty) chosen node in an SoC-specific
.dtsi, as chosen is meant for system-specific configuration.
It is already provided in microchip-mpfs-icicle-kit.dts anyway.

Fixes: 0fa6107e

 ("RISC-V: Initial DTS for Microchip ICICLE board")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>