hv: riscv: Adds initial vsbi DBCN extension

Currently dbcn outputs directly to console. Outputs to ACRN
shell vm_console when other dependencies are ready.

Tracked-On: #8841
Signed-off-by: Yifan Liu <yifan1.liu@intel.com>
Acked-by: Wang Yu1 <yu1.wang@intel.com>

hypervisor/include/arch/riscv/asm/sbi.h

@@ -20,6 +20,7 @@ enum sbi_eid  {
 	SBI_EID_HSM = 0x48534D,
 	SBI_EID_SRST = 0x53525354,
 	SBI_EID_PMU = 0x504D55,
+	SBI_EID_DBCN = 0x4442434E,
 	SBI_EID_MPXY = 0x4D505859,
 
 	/* Experimental extensions must lie within this range */
@@ -92,6 +93,11 @@ enum sbi_eid  {
 #define SBI_SRST_RESET_REASON_NONE	0x0
 #define SBI_SRST_RESET_REASON_SYSFAIL	0x1
 
+/* SBI function IDs for DBCN extension */
+#define SBI_EXT_DBCN_CONSOLE_WRITE      0x0
+#define SBI_EXT_DBCN_CONSOLE_READ       0x1
+#define SBI_EXT_DBCN_CONSOLE_WRITE_BYTE     0x2
+
 /* SBI return error codes */
 #define SBI_SUCCESS				0
 #define SBI_ERR_FAILED				-1