brcmfmac: update core reset and disable routines.

brcmfmac: update core reset and disable routines.

The original core reset and disable routines do not work always
on running system. These routines were updated to properly reset
a core. When module is unloaded the device is put into download
state where all necessary cores have been reset. This will make
sure the device is in idle mode after module unload.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>