x86: Remove usage of %ebp as a return pointer

Using %ebp as a return pointer prevents creating 'load anywhere' images
diff --git a/board/eNET/eNET_start.S b/board/eNET/eNET_start.S
index 6659549..137fe41 100644
--- a/board/eNET/eNET_start.S
+++ b/board/eNET/eNET_start.S
@@ -27,7 +27,7 @@
 .globl early_board_init
 early_board_init:
 	/* No 32-bit board specific initialisation */
-	jmp	*%ebp		/* return to caller */
+	jmp	early_board_init_ret
 
 .globl cpu_halt_asm
 cpu_halt_asm: