microblaze: Clean microblaze initialization

Move board specific function to board_init function in board/ folder
Remove externs from generic board.c
Use board_init_f function in board.c file.

Signed-off-by: Michal Simek <monstr@monstr.eu>
Acked-by: Stephan Linz <linz@li-pro.net>
diff --git a/arch/microblaze/cpu/start.S b/arch/microblaze/cpu/start.S
index 8a2f634..8564c4e 100644
--- a/arch/microblaze/cpu/start.S
+++ b/arch/microblaze/cpu/start.S
@@ -149,7 +149,7 @@
 	cmp     r6, r5, r4 /* check if we have reach the end */
 	bnei    r6, 2b
 3:	/* jumping to board_init */
-	brai	board_init
+	brai	board_init_f
 1:	bri	1b
 
 /*