Add function to change the settings of the equalization on the gbcr

Add function to change the settings of the equalization on the gbcr. Reading the setting back would also be useful. The method should be called more or less in this way: opto.gbcr1.mf_equalization(lpgbt_channel_number, value=None). If value is None, then just read back. Notice that lpgbt_channel_number=6-gbcr_channel_number. Notice also that the equalization is regulated by different register names in gbcr v2 and v3. Register names can be checked in the function implementing the 2d BER scan.