Register macro should allow a provision for specifying a reset value

[phausler]

For writable registers there should be a way of specifying a reset value which would grant a reset method.

    @Register(bitWidth: 16, reset: 0x0)
    public struct EEAR {
      @ReadWrite(bits: 0..<16, as: UInt16.self)
      public var value: VALUE
    }

that would add a method onto the register such that you can issue a reset to the contents of the register. This could perhaps be done by conforming the structure (in this case EEAR) to ResettableRegisterValue and Register has a conditional conformance that adds the public func reset() method that asks the static value from the register value type for its reset value.