dpaa2-switch: fix kdoc warnings

Running kernel-doc over the dpaa2-switch driver generates a bunch of
warnings. Fix them up by removing code comments for macros which are
self-explanatory and adding a bit more context for the
dpsw_if_get_port_mac_addr() function and the fields of the
dpsw_vlan_if_cfg structure.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>