net/cxgbe: read firmware configuration file from filesystem

net/cxgbe: read firmware configuration file from filesystem

Add support to read firmware configuration file from
/lib/firmware/cxgb4/ path in the filesystem. The firmware
config file is used to enable or disable NIC features before
firmware initialization to help retrieve better debug data to
analyze firmware init failures. The config file can also
be used to redistribute resources, like queues, TCAMs, etc.,
from disabled physical functions (PFs) to main PF, before
firmware init.

Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@chelsio.com>