cnss: Set correct boot sequence for WLAN chip

CNSS platform driver should vote for 2.7V SP2T regulator before
pulling high WLAN_EN GPIO. This is required for enabling antenna
sharing on some of the QCA6174 boards.

CRs-fixed: 754944
Change-Id: I4d202e346d8fe7852914c82aceaf9431480c3181
Signed-off-by: Prashanth Bhatta <bhattap@codeaurora.org>