i965: fix broken glBitmap + depth test

i965: fix broken glBitmap + depth test

When we use the do_blit_bitmap() function, it seems the fragment Z is always
1.0.  If depth testing is on, that means that bitmap fragments are often
occluded by other rendering.  So, the bitmap doesn't appear even if
rasterpos.Z==0.
The fix is to use the intel_texture_bitmap() path when depth testing is on.
Also, fix the incorrect Z coordinate.  It needs to be an NDC value in [-1,1].