cxgb4: Refactor t4_port_init function

Refactor t4_port_init() so that the core functionality is done by
t4_init_portinfo() for a particular port. Also rename variables to
sensible ones.

Signed-off-by: Hariprasad Shenai <hariprasad@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>