Merge master@ca9f06d087 into kernel.build.lnx.1.0

https://android.googlesource.com/platform/system/tools/mkbootimg

:
  Renames --gki_signing_extra_args to --gki_signing_signature_args
  Allow specifying avbtool path in mkbootimg
  mkbootimg: Disallow special vendor ramdisk names
  mkbootimg: Add AsciizBytes argument parser
  mkbootimg: Refactor struct constants and magic numbers
  Adding GKI signature in boot.img v4

Change-Id: Iaccd62ac298e7f91d42072e488aa223dff101cb8
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>