bnx2x: enable PMD build

bnx2x: enable PMD build

This is build infrastructure changes for bnx2x driver.
 - enable BNX2X poll mode driver in default config.
 - add it to mk
 - put entry in MAINTAINERS

Note: I intentionally did not list myself as maintainer of this
driver. QLogic has discussed taking over as maintainer.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Harish Patil <harish.patil@qlogic.com>