nir: add vs_inputs_dual_locations compiler option

Allows nir drivers to either use a single or dual locations for
vs double inputs.

i965 uses dual locations for both OpenGL and Vulkan drivers, for
now gallium OpenGL drivers only use a single location.

The following patch will also make use of this option when
calling nir_shader_gather_info().

Reviewed-by: Karol Herbst <kherbst@redhat.com>

src/amd/vulkan/radv_shader.c

@@ -67,6 +67,7 @@ static const struct nir_shader_compiler_options nir_options = {
 	.lower_extract_byte = true,
 	.lower_extract_word = true,
 	.lower_ffma = true,
+	.vs_inputs_dual_locations = true,
 	.max_unroll_iterations = 32
 };