arm: remove unneeded symbol offsets and _TEXT_BASE

Remove the last uses of symbol offsets in ARM U-Boot.
Remove some needless uses of _TEXT_BASE.
Remove all _TEXT_BASE definitions.

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
diff --git a/common/board_r.c b/common/board_r.c
index c2d0763..899f377 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -128,8 +128,8 @@
 
 static int initr_reloc_global_data(void)
 {
-#ifdef CONFIG_SYS_SYM_OFFSETS
-	monitor_flash_len = _end_ofs;
+#ifdef __ARM__
+	monitor_flash_len = _end - __image_copy_start;
 #elif !defined(CONFIG_SANDBOX)
 	monitor_flash_len = (ulong)&__init_end - gd->relocaddr;
 #endif