The active attributes are used to determine which of the vertex
attributes to enable. Matrices take up several attributes depending on
the number of column they have; this patch marks all the columns of
active matrix attributes as active.

TEST=dEQP-GLES2.functional.shaders.linkage.varying_type_mat*

BUG=angleproject:1127

Change-Id: I82f548f329f872c4e66aa0e4e71c6061a55b9987
Reviewed-on: https://chromium-review.googlesource.com/294261Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>