drm/i915: Refactor panel fitting on the LVDS. (v2)

Move the common routines into separate functions to not only increase
readability, but also throwaway surplus code.

In doing so, we review the calculation of the aspect preserving scaling
and avoid the use of fixed-point until we need to calculate the accurate
scale factor.

v2: Improve comments as suggested by Jesse.

1 files changed, 105 insertions(+), 194 deletions(-)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>