ath11k: setup QCA6390 rings for both rxdmas

For QCA6390, only one pdev is created and this pdev manages both lmacs, thus
both rxdmas. So host needs to initialize all rxdma related rings for one pdev.

Another difference is for QCA6390, host fills rxbuf to firmware and firmware
further fills the rxbuf to rxbuf ring for each rxdma.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1
Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.1.0.1-01238-QCAHKSWPL_SILICONZ-2

Signed-off-by: Carl Huang <cjhuang@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1597555891-26112-4-git-send-email-kvalo@codeaurora.org