defconfig: sdm845: Enable cnss_genl driver compilation

cnss_genl driver creates a netlink family and multicast groups
to facilitate communication between WLAN driver and userspace.

Define flag CONFIG_CNSS_GENL and set to 'y'(yes) to enable
compilation of the cnss_genl driver inorder to use the same

Change-Id: I9d81f933e4fe3c9383f213c777d335e1fe51bdd2
Signed-off-by: Srinivas Dasari <dasaris@codeaurora.org>
CRs-Fixed: 1117130