MPEG2ENC: Initialize the f_code based on supported level instead of hacked setting

MPEG2ENC: Initialize the f_code based on supported level instead of hacked setting

The f_code of MPEG2 picture parameter indicates the max search range of the
motion vector prediction. The small value will cause the unoptimized motion
vector prediction. So remove the hack setting.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
(cherry picked from commit 4fa9b3ba9d45a021e282f761d061e1151158c3ea)