Add a hang message

Make it clear that the end of the FW execution was reached without the
hand being passed to any payload.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>

lib/sbi_hart.c

@@ -196,6 +196,8 @@ int sbi_hart_init(struct sbi_scratch *scratch, u32 hartid)
 
 void __attribute__((noreturn)) sbi_hart_hang(void)
 {
+	sbi_printf("\nHang !!\n");
+
 	while (1)
 		wfi();
 	__builtin_unreachable();