[WiP] gallium: Work in progress on OpenFIMG driver

Changes:
 - disabled unused code to silence warnings,
 - implemented support for texture sampling in shaders,
 - replaced TODO warnings with DBG() messages,
 - implemented hw-specific framebuffer state,
 - separated verbose debug messages to reduce console flood,
 - fixes state emission bugs,
 - implemented basic framebuffer state emission,
 - added missing screen param queries,
 - fixed definition COLOR_MODE field of FGPF_FBCTL register.