sysupgrade: Add SBL_NAND_PREAMBLE if preamble bytes exist in image

Now we are adding preamble value to read SBL header if ubi section
is present in the image. But in case of NOR+NAND images, though we are
having SBL in NOR and ubi section is also present and NAND_PREAMBLE
is getting added. which is breaking NOR+NAND sysupgrade.

Added functionality to compare first 12 bytes of section with pre
defined PREAMBLE value. If values matches, add the NAND_PREAMBLE to
read SBL header.

Change-Id: I704ee86cc50aa3ce3b2ab6ec34beab866ffde4b9
Signed-off-by: Anto Norbert <norbrt@codeaurora.org>
diff --git a/tools/sysupgrade.h b/tools/sysupgrade.h
index 3c158d7..2be2760 100644
--- a/tools/sysupgrade.h
+++ b/tools/sysupgrade.h
@@ -126,3 +126,4 @@
 int is_component_authenticated(char *, char *, char *);
 int is_image_authenticated(void);
 int do_board_upgrade_check(char *);
+int check_nand_preamble(uint8_t *);