Don't check WAYLAND_SCANNER if wayland isn't used or found

Don't check WAYLAND_SCANNER if wayland isn't used or found

checking for WAYLAND... no
checking for LIBVA_WAYLAND_DEPS... no
checking for pkg-config... (cached) /usr/bin/pkg-config
checking pkg-config is at least version 0.9.0... yes
checking for WAYLAND_SCANNER... no
configure: error: Package requirements (wayland-scanner) were not met:

No package 'wayland-scanner' found

Signed-off-by: Xiang, Haihao <haihao.xiang@intel.com>
Reviewed-by: Sean V Kelley <sean.v.kelley@intel.com>