broadcom: Move the Broadcom drivers

Moves the drivers for Broadcom devices into
drivers/net/ethernet/broadcom/ and the necessary Kconfig and Makefile
changes.

CC: Eilon Greenstein <eilong@broadcom.com>
CC: Michael Chan <mchan@broadcom.com>
CC: Matt Carlson <mcarlson@broadcom.com>
CC: Gary Zambrano <zambrano@broadcom.com>
CC: "Maciej W. Rozycki" <macro@linux-mips.org>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>