fdt: boot_get_fdt: android: compress handling (non-functional)

Prepare for booting Android images which lack any DTB in the second
area by using 'fdtaddr' environment variable as source/address of FDT.
No functional/behavioral change expected in this patch.

Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Simon Glass <sjg@chromium.org>