riscv: Add a SYSCON driver for Andestech's PLIC

The Platform-Level Interrupt Controller (PLIC)
block holds memory-mapped claim and pending registers
associated with software interrupt. It is required
for handling IPI.

Signed-off-by: Rick Chen <rick@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 3a4470d..511768b 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -109,6 +109,15 @@
 	  The SiFive CLINT block holds memory-mapped control and status registers
 	  associated with software and timer interrupts.
 
+config ANDES_PLIC
+	bool
+	depends on RISCV_MMODE
+	select REGMAP
+	select SYSCON
+	help
+	  The Andes PLIC block holds memory-mapped claim and pending registers
+	  associated with software interrupt.
+
 config RISCV_RDTIME
 	bool
 	default y if RISCV_SMODE