drm/ci: mediatek: Test both GPU and display drivers

Mediatek 8173 and 8183 SOCs have a separate display controller
and GPU, with different drivers for each. Add support in drm-ci
to test both these drivers.

Since powervr support is not yet added in igt-gpu-tools, disable
the mt8173-gpu job which uses powervr driver.

Signed-off-by: Vignesh Raman <vignesh.raman@collabora.com>