ath11k: Add direct buffer ring support

Add direct buffer ring (dbring) with helper API, which is used by the
spectral scan. Initialise the direct buffer ring based on the dma ring
capability, which get announced in the wmi service ready extended event.
This ring is slightly changed from data path rings. Compare to data path
ring this ring shares the hp and tp address to firmware though WMI commands.
Also the replenish buffer size is derived from firmware announcement.
driver receive indication through WMI event
WMI_PDEV_DMA_RING_BUF_RELEASE_EVENTID.

Tested-on: IPQ8074 WLAN.HK.2.1.0.1-01228-QCAHKSWPL_SILICONZ-1

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1591688014-26441-1-git-send-email-periyasa@codeaurora.org