anv: Enabled the VK_EXT_sample_locations extension

Enabled the VK_EXT_sample_locations for Intel Gen >= 7.

v2: Replaced device.info->gen >= 7 with True, as Anv doesn't support
    anything below Gen7. (Lionel Landwerlin)

Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <!1887>