Merge remote-tracking branch 'remotes/kevin/tags/for-upstream' into staging

Multiboot patches

# gpg: Signature made Wed 07 Mar 2018 11:15:17 GMT
# gpg:                using RSA key 7F09B272C88F2FD6
# gpg: Good signature from "Kevin Wolf <[email protected]>"
# Primary key fingerprint: DC3D EB15 9A9A F95D 3D74  56FE 7F09 B272 C88F 2FD6

* remotes/kevin/tags/for-upstream:
  multiboot: fprintf(stderr...) -> error_report()
  multiboot: Use header names when displaying fields
  multiboot: Remove unused variables from multiboot.c
  multiboot: bss_end_addr can be zero

Signed-off-by: Peter Maydell <[email protected]>