pkgbase: Create a cxgbe-tools package

cxgbetool is only useful for users who have a Chelsio card.
Create a package for it so users that don't have this card can
avoid having this program.

Differential Revision: https://reviews.freebsd.org/D31793

(cherry picked from commit b8876cac2d230098b902e7f927ef170312a06c03)