cxgb4/cxgb4vf: Cleanup macros, add comments and add new MACROS

Cleanup few MACROS left out in t4_hw.h to be consistent with the
existing ones. Also replace few hardcoded values with MACROS. Also
update comments for some code

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