mesa: Add skeleton implementations of glInvalidateTex{Sub,}Image

mesa: Add skeleton implementations of glInvalidateTex{Sub,}Image

These are part of GL_ARB_invalidate_subdata (but not OpenGL ES 3.0).

v2: Add comment explaining why minimum dimensions are set to 1 for some
texture targets.  Add default case to switch statement to silence
compiler warnings and detect new texture targets.  Both changes
suggested by Brian.  Also use _mesa_is_desktop_gl as suggested by Ken.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>