console: move chardev declarations to sysemu/char.h

move generic chardev APIs to sysemu/char.h, to make them available to
callers which can not depend on the whole of ui/console.h.
This fixes a build error on systems without pixman-devel:

./configure --disable-tools --disable-docs --target-list=arm-linux-user
...
pixman            none
...
make
...
In file included from
/data/home/nchip/linaro/qemu/include/ui/console.h:4:0,
                 from /data/home/nchip/linaro/qemu/stubs/vc-init.c:2:
/data/home/nchip/linaro/qemu/include/ui/qemu-pixman.h:14:20: fatal
error: pixman.h: No such file or directory
 #include <pixman.h>
                    ^
compilation terminated.

Reported-by: Riku Voipio <riku.voipio@iki.fi>
Tested-by: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-id: 1403508500-32691-1-git-send-email-mst@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>