gma500: remove unused drm_psb_no_fb

commit f9f23a77(gma500: remove no_fb bits)
remove all the drm_psb_no_fb relations code in gma500 except this line code,
so remove it also.

Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>