riscv: clarify error message on undefined exceptions

Undefined exceptions are treated as reserved. This is not clearly
communicated to the user. Adjust the error message to clarify that a
reserved exception has occurred and add additional details.

Fixes: e8b522b ("riscv: treat undefined exception codes as reserved")
Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

arch/riscv/lib/interrupts.c

@@ -37,7 +37,8 @@ static void _exit_trap(ulong code, ulong epc, struct pt_regs *regs)
 		printf("exception code: %ld , %s , epc %lx , ra %lx\n",
 		       code, exception_code[code], epc, regs->ra);
 	} else {
-		printf("Reserved\n");
+		printf("reserved exception code: %ld , epc %lx , ra %lx\n",
+		       code, epc, regs->ra);
 	}
 
 	hang();