ath10k: enable bus layer suspend/resume for WCN3990

Register snoc bus layer suspend/resume PM ops and configure
the wakeup source(CE2) for the device.

Testing:
    Tested on WCN3990 HW.
    Tested FW: WLAN.HL.2.0-01192-QCAHLSWMTPLZ-1.

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