wayland: Fix wayland-tools packaging

There are some packaging problems due to the wayland-tools packaging
implementation. The wayland-tools package currently looks like this:

wayland-tools
└── usr
    ├── bin
    │   └── wayland-scanner
    └── share
        └── wayland
            ├── wayland.dtd
            ├── wayland-scanner.mk
            └── wayland.xml

The files wayland.dtd and wayland.xml belong in the main package,
while wayland-scanner.mk belongs in wayland-dev.

Fix the wayland.dtd and wayland.xml packaging by prepending the
wayland-tools package and dropping the main package FILES variable
override. The file wayland-scanner.mk is included in the main
package by default, and so must be explicitly added to wayland-dev.

Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit a31fbec4)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>