riscv: add UltraRISC SoC family Kconfig support

The first SoC in the UltraRISC series is UR-DP1000, containing octa
UltraRISC CP100 cores.

Signed-off-by: Jia Wang <wangjia@ultrarisc.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20260427-ultrarisc-pcie-v4-1-98935f6cdfb5@ultrarisc.com
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: WangJia-UR

arch/riscv/Kconfig.socs

@@ -84,6 +84,12 @@ config ARCH_THEAD
 	help
 	  This enables support for the RISC-V based T-HEAD SoCs.
 
+config ARCH_ULTRARISC
+	bool "UltraRISC RISC-V SoCs"
+	help
+	  This enables support for UltraRISC SoC platform hardware,
+	  including boards based on the UR-DP1000.
+
 config ARCH_VIRT
 	bool "QEMU Virt Machine"
 	select POWER_RESET