microblaze: Enable early printk only for uartlite

Microblaze has support for early printk. The second serial
driver (uart16550/8250) has no microblaze support for early
printk.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/Kconfig.debug

@@ -10,6 +10,7 @@ source "lib/Kconfig.debug"
 
 config EARLY_PRINTK
 	bool "Early printk function for kernel"
+	depends on SERIAL_UARTLITE_CONSOLE
 	default n
 	help
 	  This option turns on/off early printk messages to console.