drivers: lpadc: Make DT props match RM

- Remove build asserts in favor of DT enums
- Remove power level property since it is unused by SDK
- Correct voltage ref value in DT to correspond to
  chip specific values documented in reference manuals
  instead of corresponding to SDK enum names.
- Fix SOC devicetrees affected by these changes.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>