v3d: Include supported DXT formats to enable s3tc/dxt extensions

v3d: Include supported DXT formats to enable s3tc/dxt extensions

DXT1_RGBA and sRGB variants of DXT[135] formats are enabled as
valid format on V3D.

Once all S3TC formats supported by V3C are enabled the following
extensions become exposed by gallium.

    * GL_ANGLE_texture_compression_dxt3
    * GL_ANGLE_texture_compression_dxt5,
    * GL_EXT_texture_compression_dxt1
    * GL_EXT_texture_compression_s3tc
    * GL_S3_s3tc
    * GL_EXT_texture_compression_s3tc_srgb

This enables 206 passing piglit test related to gl_compressed.*s3tc_dxt

Cc: 20.0 20.1 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4934>