glsl/ir: add param index to variable.

glsl/ir: add param index to variable.

We have a requirement to store the index into the mesa parameterlist
for uniforms. Up until now we've overwritten var->data.location with
this info. However this then stops us accessing UniformStorage,
which is needed to do proper dereferencing.

Add a new variable to ir_variable to store this value in, and change
the two uses to use it correctly.

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>