anv: turn on samplerAnisotropy in VkPhysicalDeviceFeatures

anv: turn on samplerAnisotropy in VkPhysicalDeviceFeatures

According to the Vulkan spec 5.63.4 :

  samplerAnisotropy indicates whether anisotropic filtering is supported. If
  this feature is not enabled, the maxAnisotropy member of the
  VkSamplerCreateInfo structure must be 1.0.

Since we already set maxAnisotropy to 16 and program the hardware according
to the VkSamplerCreateInfo.maxAnisotropy, it seems we can turn this on.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>