drm/msm/adreno: Add adreno family

Sometimes it is useful to know the sub-generation (or "family").  And in
any case, this helps us get away from infering the generation from the
numerical chip-id.

v2: Fix is_a2xx() typo

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/549773/