cnss2: Use proper way to enable FW waltest

Currently CNSS driver enables FW waltest by avoiding calling host
driver probe during host driver loading. If host driver loading
waits for probe to complete, this method won't work. Enable FW
waltest using proper way by sending QMI waltest mode request to FW.

Change-Id: I9ca8d7cbc4479a57b775dd54a2fcf61036f44799
CRs-fixed: 2024543
Signed-off-by: Yue Ma <yuem@codeaurora.org>