nios2: enlarge the code relocation range

As we will use u-boot-dtb.bin, the code relocation range
should be adjusted to accommodate the additional dtb.
It might be overkilled to look into dtb header to find the
dtb size, so we will simply use CONFIG_SYS_MONITOR_LEN.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>

arch/nios2/cpu/start.S

@@ -73,8 +73,9 @@ _cur:	movhi	r5, %hi(_cur - _start)
 	ori	r5, r5, %lo(_start)	/* r5 <- linked _start */
 	beq	r4, r5, 3f
 
-	movhi	r6, %hi(_edata)
-	ori	r6, r6, %lo(_edata)
+	movhi	r6, %hi(CONFIG_SYS_MONITOR_LEN)
+	ori	r6, r6, %lo(CONFIG_SYS_MONITOR_LEN)
+	add	r6, r6, r5
 2:	ldwio	r7, 0(r4)
 	addi	r4, r4, 4
 	stwio	r7, 0(r5)