Until right now we were using glTexImage*D for any compressed
internalformat. That would only work always if the driver supports
online compression for specific compressed internalformats.

As it is not really easy to check which internalformats the driver
supports online compression for, it is safer to use
glCompressedTexImage*D for any specific internalformat, keeping
glTexImage*D for the generic ones.

v2: specific compressed internalformat GL_COMPRESSED_RED_RGTC1 was
    missing, minor tweaks (Antia)

Reviewed-by: Antia Puentes <apuentes@igalia.com>