ath11k: setup ce tasklet for control path

CE srng is used for control path and CE srng processing is done using tasklet
bottom half. Setup ce tasklet initialization and scheduling for control path.

Needed for PCI support.

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: Govind Singh <govinds@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1597389030-13887-7-git-send-email-kvalo@codeaurora.org