Merge remote-tracking branch 'remotes/dgibson/tags/isa-cleanup-20170206' into staging

Merge remote-tracking branch 'remotes/dgibson/tags/isa-cleanup-20170206' into staging

Allow ISA to be disabled on some platforms (v3)

This makes some cleanups that are a start on allowing ISA to be
compiled out for platforms which don't use it.

I posted this series last November, and it collected a number of R-bs
and no apparent objections.  So, I've now rebased it (trivially) and
am sending a pull request in the hopes of merge.  A lot of the pieces
here don't have a clear maintainer, so I'm sending it directly to
Peter.

Notes:
  * Patch 3/3 triggers a style warning, but that's just because I'm
    moving a C++ // comment verbatim from one file to another

Changes since v2:
  * Trivial rebase

Changes since v1:
  * Fixed some silly compile errors in 3/3 exposed by some
    changes in other headers

# gpg: Signature made Mon 06 Feb 2017 01:37:50 GMT
# gpg:                using RSA key 0x6C38CACA20D9B392
# gpg: Good signature from "David Gibson <david@gibson.dropbear.id.au>"
# gpg:                 aka "David Gibson (Red Hat) <dgibson@redhat.com>"
# gpg:                 aka "David Gibson (ozlabs.org) <dgibson@ozlabs.org>"
# gpg:                 aka "David Gibson (kernel.org) <dwg@kernel.org>"
# Primary key fingerprint: 75F4 6586 AE61 A66C C44E  87DC 6C38 CACA 20D9 B392

* remotes/dgibson/tags/isa-cleanup-20170206:
  Split ISA and sysbus versions of m48t59 device
  Allow ISA bus to be configured out
  Split serial-isa into its own config option

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