I had the same problem too... It is not a problem of the BIOS, it is a touch pad driver issue.
How I worked it out:
Downloaded an older version of the driver from the Dell's website (16.3.7.0,A03).
Uninstalled Dell Touchpad Software (Synaptics) from computer.
Rebooted.
Installed the new (older) downloaded driver.
Rebooted.
The two finger tapping worked again even with the latest BIOS.
Hope that it helps... 