brcmfmac: SDIO: avoid using bus state for private states.

Each bus driver is maintaing an exported bus state indicating
if upper layers can or cannot send data. SDIO is using this state
also for more private states. This makes handling the states and
state changes complex. This patch minimises the exposed states
and makes SDIO keep track of an internal state where necessary.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>