st/mesa: fix bitmap texture target code and simplify tex sampler state

st/mesa: fix bitmap texture target code and simplify tex sampler state

Bitmaps may be drawn with a PIPE_TEXTURE_2D or PIPE_TEXTURE_RECT resource
as determined at context creation by checking if PIPE_CAP_NPOT_TEXTURES is
supported.  But many places in the bitmap code were hard-coded to use
PIPE_TEXTURE_2D.  Use st->internal_target instead.

I think an older NV chip is the only case where a gallium driver does not
support NPOT textures.  Bitmap drawing was probably broken for that GPU.

Also, we only need one sampler state with texcoord normalization set up
according to st->internal_target.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>