imx-base.inc: Add virtual/libopenvg to MACHINE_{ARCH,SOCARCH}_FILTER

imx-base.inc: Add virtual/libopenvg to MACHINE_{ARCH,SOCARCH}_FILTER

The virtual/libopenvg is provided by the GPU packages and needs to be
used for the dynamic package architecture.

The issue has been identified while debugging a build failure in
fsl-gpu-sdk. It was using the common architecture instead of the right
architecture.

Now mx6q, mx6dl and mx6sx use MACHINE_SOCARCH and mx6sl MACHINE_ARCH
for all packages depending on virtual/libopenvg.

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