weston: Add missing runtime dependency on freerdp

weston: Add missing runtime dependency on freerdp

With rdp enabled, nothing from freerdp is installed in the rootfs, and
rdp is not usable. It seems there is no actual build time dependency
other than the meson check itself, so add an explicit runtime
dependency.

Signed-off-by: Tom Hochstein <tom.hochstein@oss.nxp.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>