microblaze: Support early console on uart16550

Early console support reuse setting from U-BOOT that's why
it is not necessary to setup baudrates, etc.

Signed-off-by: Michal Simek <monstr@monstr.eu>
diff --git a/arch/microblaze/include/asm/prom.h b/arch/microblaze/include/asm/prom.h
index 101fa09..bdc3831 100644
--- a/arch/microblaze/include/asm/prom.h
+++ b/arch/microblaze/include/asm/prom.h
@@ -27,6 +27,7 @@
 
 /* Other Prototypes */
 extern int early_uartlite_console(void);
+extern int early_uart16550_console(void);
 
 #ifdef CONFIG_PCI
 /*