chardev: move headers to include/chardev

So they are all in one place. The following patch will move serial &
parallel declarations to the respective headers.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 7df0882..48e2964 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1238,6 +1238,7 @@
 M: Marc-André Lureau <marcandre.lureau@redhat.com>
 S: Maintained
 F: chardev/
+F: include/chardev/
 F: backends/msmouse.c
 F: backends/testdev.c