cxgbe(4): Break up t4_read_chip_settings.

Read the PF-only hardware settings directly in get_params__post_init.
Split the rest into two routines used by both the PF and VF drivers: one
that reads the SGE rx buffer configuration and another that verifies
miscellaneous hardware configuration.

Sponsored by: Chelsio Communications

(cherry picked from commit fae028dd97d8fc8f9ba5153408b177481dbefd70)