Fix yang-parser-impl not being pulled

sal-netconf-connect depends on it, but relies on in transiently via
yang-data-impl. That transient dependency is going away, so introduce a
proper dependency.

Change-Id: I9efbec70e5630c98d19cd113a7d7096739f90dac
Signed-off-by: Robert Varga <rovarga@cisco.com>