Retrofitted boot v2 has concatenated vendor & generic ramdisk

Layout of a retrofitted v2 boot image:
  +---------------------+
  | boot header         | 1 page
  +---------------------+
  | kernel              | n pages
  +---------------------+
  | vendor ramdisk ||   |
  | generic ramdisk     | m pages
  +---------------------+
  | second stage        | o pages
  +---------------------+
  | recovery dtbo/acpio | p pages
  +---------------------+
  | dtb                 | q pages
  +---------------------+

The "ramdisk" section actually contains the concatenated vendor &
generic ramdisk, and the generic ramdisk MUST be at the end.
Extract only the "generic ramdisk" part for VTS validation.

Bug: 211741246
Test: m vts_gki_compliance_test
Change-Id: Ic47e2cfcbfd3045c8279b343684787404eb224b7
1 file changed