Instead of using two tables to estimate the temporal decimation
factor, use a formula. This allows to get the closest fps, which
sounds better than the current tables.

Also, the current code doesn't store the real framerate.

This patch fixes the above issues.

[Ezequiel:
  - introduce a TW686X_MAX_FPS macro for max_fps.
  - use hweight_long instead of open coding the set bits count.]
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>