net: ipa: define the ENDP_INIT_NAT register

Define the ENDP_INIT_NAT register for setting up the NAT
configuration for an endpoint.  We aren't using NAT at this
time, so explicitly set the type to BYPASS for all endpoints.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>