st/mesa: check texture target in allocate_full_mipmap()
st/mesa: check texture target in allocate_full_mipmap()

Some kinds of textures never have mipmaps.  3D textures seldom have
mipmaps.

Reviewed-by: José Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler