drm/gma500/psb: Make use of generic clock code

Add chip specific callbacks for the generic and non-generic clock
calculation code. Also remove as much dupilicated code as possible.

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

diff --cc drivers/gpu/drm/gma500/psb_device.c
Simple merge

diff --cc drivers/gpu/drm/gma500/psb_device.h
Simple merge

diff --cc drivers/gpu/drm/gma500/psb_intel_display.c
Simple merge

diff --cc drivers/gpu/drm/gma500/psb_intel_display.h
Simple merge