When we need to add the standard timing mode, we will firstly check whether it
can be found in DMT table by comparing the hdisplay/vdisplay/vfresh_rate.
If it can't be found, then we will use the cvt/gtf to add the required mode.
If it can be found, it will be returned.

At the same time the function of drm_mode_vrefresh is also fixed. It will
return the result of actual refresh_rate plus 0.5.
For example:
When the calculated value is 84.9, then the fresh_rate is 85.
When the calculated value is 70.02, then the fresh_rate is 70.
Signed-off-by: NZhao Yakui <yakui.zhao@intel.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>