This fixes the virtfs documentation (LP 1581976), deprecates the
-virtfs_synth command line option, along with some assorted cleanups.

# gpg: Signature made Fri 17 May 2019 19:29:40 BST
# gpg:                using RSA key B4828BAF943140CEF2A3491071D4D5E5822F73D6
# gpg: Good signature from "Greg Kurz <groug@kaod.org>" [full]
# gpg:                 aka "Gregory Kurz <gregory.kurz@free.fr>" [full]
# gpg:                 aka "[jpeg image of size 3330]" [full]
# Primary key fingerprint: B482 8BAF 9431 40CE F2A3  4910 71D4 D5E5 822F 73D6

* remotes/gkurz/tags/for-upstream:
  virtfs: Fix documentation of -fsdev and -virtfs
  vl: Deprecate -virtfs_synth
  fsdev: Error out when unsupported option is passed
  fsdev: Move some types definition to qemu-fsdev.c
  fsdev: Drop unused opaque field
  fsdev: Drop unused extern declaration

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

# Conflicts:
#	qemu-deprecated.texi