ath10k: introduce CE_ATTR_POLL attribute for polling pipe

Existing copy engine interrupt enable logic assumes that last
CE is using polling mode and due to this interrupt for last copy engine
are always disabled. WCN3990 uses last CE for pktlog and
interrupt remains disabled with existing logic.

To mitigate this issue, introduce CE_ATTR_POLL flag and control
the interrupt based on the flag which can be set in ce_attr.

Testing:
    Tested on WCN3990 and QCA6174 HW.
    Tested FW: WLAN.HL.2.0-01192-QCAHLSWMTPLZ-1,
               WLAN.RM.4.4.1-00109-QCARMSWPZ-1

Signed-off-by: Govind Singh <govinds@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>