package/xen: Backport a header include fix for makedev

maekdev() is available from sys/types.h but only due to a bug in glibc. This
is being fixed by printing an error when using makedev() from sys/types.h.
To fix the issue we should include sys/sysmacros.h for makedev(). As this
has already been fixed in upstream Xen we can backport the patch.

Fixes:
    http://autobuild.buildroot.net/results/552/552e66d764885341b2fe208a0e4382b5fe05ea9d/



Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>