mmc: add SDIO identifiers for Broadcom WLAN devices

The SDIO identifier for Broadcom WLAN devices were defined in the
brcmfmac SDIO driver. Moving the definitions in MMC header file
seems common sense.

Reviewed-by: Hante Meuleman <meuleman@broadcom.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>