freescale-imx: add BR2_PACKAGE_FREESCALE_IMX_HAS_VPU config

freescale-imx: add BR2_PACKAGE_FREESCALE_IMX_HAS_VPU config

Since the imx-vpu package build is skipped if the platform doesn't
have a VPU, libraries dependent on the package such as libimxvpuapi
can fail although the imx-vpu package build went "fine".

This patch therefore adds a BR2_PACKAGE_FREESCALE_IMX_HAS_VPU config
which is used in every package selecting imx-vpu directly or indrectly.

It fixes the following build errors:
http://autobuild.buildroot.net/results/892/8924b17f3aa5eba1a8016d84d4478ecb0a96b236/
http://autobuild.buildroot.net/results/86f/86fef2a30065d5bc0d7755706e9ca3332426834d/
http://autobuild.buildroot.net/results/b47/b47eb03e93e2f1af85caebb707f7b4667f7e3d74/
http://autobuild.buildroot.net/results/4c9/4c9b22b33533132fd9f88917cc341ae2c2e171a8/
http://autobuild.buildroot.net/results/a8b/a8b33bfd099d9b9cd383cc568ea70846eb13c34d/

Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>