i386/pc: move vmmouse.c to hw/i386/

It's a x86-only device, so it does not make sense to keep it
in the shared misc folder.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>