package/freescale-imx/imx-gpu-viv: is an libopencl provider

The imx-gpu-viv install libOpenCL.so.1.2 library and cl.h header,
so declare it as a libopencl provider.

With this support we can select the clinfo package provided by
Buildroot instead of the one provided by imx-gpu-viv package.

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>