gallium/hud: do not use texture-rect for font

RECT textures used to be required to be supported by drivers. But since the state-tracker learned how to lower these to 2D textures, some drivers no longer support them.

While we have lowering in place for this, lowering it involves some needless overhead. So let's just use a 2D texture instead of a RECT texture.

Because having two versions and switching between them is more complicated than it needs to be, let's just always use a 2D texture. Similarly, let's just always multiply the reciprocal here, so we don't have to test for PIPE_CAP_TGSI_DIV first.