aux: Rename aux.[ch] to auxbus.[ch] for the benefit of Windows

On Windows 'aux.*' is a reserved name and cannot be used for
filenames; see
  https://msdn.microsoft.com/en-gb/library/windows/desktop/aa365247(v=vs.85).aspx

This prevents cloning the QEMU git repo on Windows:

C:\Java\sources\kvm> git clone https://github.com/qemu/qemu.git
Cloning into 'qemu'...
remote: Counting objects: 279563, done.
remote: Total 279563 (delta 0), reused 0 (delta 0), pack-reused 279563R
Receiving objects: 100% (279563/279563), 122.45 MiB | 3.52 MiB/s, done.
Resolving deltas: 100% (221942/221942), done.
Checking connectivity... done.
error: unable to create file hw/misc/aux.c (No such file or directory)
error: unable to create file include/hw/misc/aux.h (No such file or directory)
Checking out files: 100% (4795/4795), done.
fatal: unable to checkout working tree
warning: Clone succeeded, but checkout failed.
You can inspect what was checked out with 'git status'
and retry the checkout with 'git checkout -f HEAD'

(bug https://bugs.launchpad.net/bugs/1595240)

Rename the offending files for the benefit of Windows.

Reported-by: Алексей Курган <akurgan@yandex.ru>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Wei Huang <wei@redhat.com>
Tested-by: KONRAD Frederic <fred.konrad@greensocs.com>
Message-id: 1467377145-32385-1-git-send-email-peter.maydell@linaro.org
