packagegroup-fsl-tools-gpu: Stop installing fsl-gpu-sdk for non-X11 backends

The fsl-gpu-sdk is broken for all backends but X11 so we ensure to
include it only when 'x11' distro feature is in use.

The failure has been found when building the 'fsl-image-machine-test'
for all backends at O.S. Systems for testing, this is not a fix but a
workaround and I expect this to be fixed by Freescale in an upcoming
release.

Change-Id: Ica6821a66de7bedb87510ac171ff1b7ba383b21b
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>