brcmfmac: remove unnecessary function prototypes

With the merge of bcmsdh.c and bcmsdh_mmc.c several function prototypes
are no longer necessary and can be removed. Consequence is reordering
some of the functions.

Reviewed-by: Franky Lin <frankyl@broadcom.com>
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>