brcmfmac: add support for dma indices feature

PCIe full dongle firmware can support a dma indices feature with which
firmware can update/fetch the read/write indices of message buffer
rings on both host to dongle and dongle to host directions. The support is
announced by firmware through shared flags.

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: Kalle Valo <kvalo@codeaurora.org>