brcmsmac: add support for BCM4313 iPA variant

This patch completes the changes needed for supporting the
iPA variant cards of the BCM4313 wireless chipset.

Tested-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>