find dtb in android boot image with header version 2 during bootm

find dtb in android boot image with header version 2 during bootm

This patch is about bootm process, android boot image and device tree.

Android 10 updates the boot image header to version 2,
which includes a section to store the device tree blob (DTB) image.

include/android_image.h has updated the struct andr_img_hdr,
but not used in bootm process. This patch avoid reporting
"Device tree not found or missing FDT support"
when bootm a correctly constructed android boot image.

Signed-off-by: chenshuo <chenshuo@eswin.com>