common: board_f: change calculation of gd->mon_len to fix s5p4418 reloc

ARCH_NEXELL: Change calculation of monitor length (gd->mon_len) to fix
relocation at boards with s5p4418-SoC (ARCH_NEXELL). At s5p4418, _start
is after the header (NSIH). Therefore the monitor length has to be
calculated using __image_copy_start instead of _start in order the
whole monitor code is relocated.

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
diff --git a/common/board_f.c b/common/board_f.c
index 7e31369..8bada6f 100644
--- a/common/board_f.c
+++ b/common/board_f.c
@@ -282,7 +282,9 @@
 
 static int setup_mon_len(void)
 {
-#if defined(__ARM__) || defined(__MICROBLAZE__)
+#if defined(CONFIG_ARCH_NEXELL)
+	gd->mon_len = (ulong)__bss_end - (ulong)__image_copy_start;
+#elif defined(__ARM__) || defined(__MICROBLAZE__)
 	gd->mon_len = (ulong)__bss_end - (ulong)_start;
 #elif defined(CONFIG_SANDBOX) && !defined(__riscv)
 	gd->mon_len = (ulong)_end - (ulong)_init;