Makefile: Add U_BOOT_TZ and include in version

Define U_BOOT_TZ alongside U_BOOT_TIME and U_BOOT_DATE and use it to
include the timezone in the version output.

Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Chris Packham <judge.packham@gmail.com>
diff --git a/Makefile b/Makefile
index bc47d98..3869728 100644
--- a/Makefile
+++ b/Makefile
@@ -1232,7 +1232,8 @@
 
 define filechk_timestamp.h
 	(LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \
-	LC_ALL=C date +'#define U_BOOT_TIME "%T"')
+	LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \
+	LC_ALL=C date +'#define U_BOOT_TZ "%z"')
 endef
 
 $(version_h): include/config/uboot.release FORCE