[adc5g] Changes to reset logic.

The MMCM is now reset using dcm_reset instead of ctrl_reset, this signal is driven high
by the OPB pcore right after reset.

The FIFO is reset when the MMCM is not yet locked or when ctrl_reset is driven high by
the OPB pcore. This is controllable via software.
[adc5g] Expanded the o0_allowed values to include 1.0 for the MMCM.

This was previously set to 2:128 but 1 is actually an allowable value.
Also simplified xps_adc5g.m by using the ismember function instead of
checking if MMCM parameters are within the top/bottom of allowable
values.