dt: bindings: add bindings for Broadcom bcm43xx sdio devices

The Broadcom bcm43xx sdio devices are fullmac devices that may be
integrated in ARM platforms. Currently, the brcmfmac driver for
these devices support use of platform data. This patch specifies
the bindings that allow this platform data to be expressed in the
devicetree.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
[hdegoede@redhat.com: drop clk / reg_on gpio handling, as there is no consensus
 on how to handle this yet]
[hdegoede@redhat.com: move from bindings/staging to bindings]
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>