block/file-posix: Simplify the XFS_IOC_DIOINFO handling

The handling for the XFS_IOC_DIOINFO ioctl is currently quite excessive:
This is not a "real" feature like the other features that we provide with
the "--enable-xxx" and "--disable-xxx" switches for the configure script,
since this does not influence lots of code (it's only about one call to
xfsctl() in file-posix.c), so people don't gain much with the ability to
disable this with "--disable-xfsctl".
It's also unfortunate that the ioctl will be disabled on Linux in case
the user did not install the right xfsprogs-devel package before running
configure. Thus let's simplify this by providing the ioctl definition
on our own, so we can completely get rid of the header dependency and
thus the related code in the configure script.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211215125824.250091-1-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>