brcmfmac: move chip download state code to sdio_chip.c

brcmfmac: move chip download state code to sdio_chip.c

enter/exit download state routine is going to diverge with new ARM core
introduced. Move corresponding code to sdio_chip.c for new ARM core support.

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