ARM: dts: cubox-i: add support for Broadcom Wifi/Bluetooth devices

Add DT support for the Broadcom Wifi/Bluetooth devices found on the
microsom board.

[Modified original Russell King's patch to use mmc-pwrseq]

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Tested-by: Jon Nettleton <jon@solid-run.com>
Tested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>