microblaze: Add support for early console on mdm

Support mdm early console:
 - extend time for retries
 - add mdm compatible property

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/kernel/prom.c b/arch/microblaze/kernel/prom.c
index 18d9371..977484a 100644
--- a/arch/microblaze/kernel/prom.c
+++ b/arch/microblaze/kernel/prom.c
@@ -88,7 +88,8 @@
 		}
 		if ((strncmp(p, "xlnx,xps-uartlite", 17) == 0) ||
 				(strncmp(p, "xlnx,opb-uartlite", 17) == 0) ||
-				(strncmp(p, "xlnx,axi-uartlite", 17) == 0)) {
+				(strncmp(p, "xlnx,axi-uartlite", 17) == 0) ||
+				(strncmp(p, "xlnx,mdm", 8) == 0)) {
 			unsigned int *addrp;
 
 			*(u32 *)data = UARTLITE;