riscv: cache: Add CBO instructions

Define CBO inval and flush instructions and use those for the
dcache inval and flush operations respectively.

Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index f4384d1..043d963 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -319,6 +319,10 @@
 	help
 	  Adds "A" to the ISA string passed to the compiler.
 
+config RISCV_ISA_ZICBOM
+	bool "Zicbom support"
+	depends on !SYS_DISABLE_DCACHE_OPS
+
 config DMA_ADDR_T_64BIT
 	bool
 	default y if 64BIT