Add support for paritycheck

[Silicon1602]

Using the paritycheck keyword will not add any logic to internal or external registers. Section 9.10 of the LRM describes this field as follows:

c) The paritycheck property can be applied to a field to indicate it should be covered and checked by parity.
1) The default is false (no check occurs).
2) Not all fields in a register need to have the same paritycheck property value.
3) Parity is calculated each cycle on the next value of every qualifying bit and the result is stored.
4) Parity is checked each cycle by comparing the generated parity on the current value of each qualifying bit with the stored parity result. A parity_error output for the addrmap is set to 1 when the generated value and stored parity do not match.