cmd: Kconfig: Change dependency for CMD_ADC

CMD_ADC selected DM_REGULATOR unconditionally without enabling DM.
That's why change select to depends on to cover it.

Kconfig is showing this issue as:
WARNING: unmet direct dependencies detected for REGMAP
  Depends on [n]: DM [=n]
  Selected by [y]:
  - DM_REGULATOR_PBIAS [=y] && DM_REGULATOR [=y]

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Update CMD_ADC=y configs to enable DM_REGULATOR now]
Signed-off-by: Tom Rini <trini@konsulko.com>