bnxt_en: add TC flower offload flow_alloc/free FW cmds

This patch adds the hwrm_cfa_flow_alloc/free() routines
that are needed to issue the FW cmds needed for TC flower offload.

Signed-off-by: Sathya Perla <sathya.perla@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>