wcnss: Add API to expose the IRIS XO mode set

IRIS XO mode can be configured thru module parameter; and it can also
be auto detected. Add an API to expose the IRIS XO mode set. WLAN driver
can use this API for it's XO specific operation.

Change-Id: If40ae715f5e400e13a6fc9588d2bd144958ee8c2
Signed-off-by: Sameer Thalappil <sameert@codeaurora.org>