brcm80211: select WANT_DEV_COREDUMP conditionally for brcmfmac

CONFIG_BRCMDBG selects WANT_DEV_COREDUMP but is only used by
brcmfmac so reflect that in the Kconfig.

Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>