qcacmn: Replace DEBUG macro with WLAN_DEBUG
This is a qcacld-2.0 to qcacld-3.0 propagation.
pr_debug() should not appear by default in kernel log (kmsg).
DEBUG is a kernel macro, since host driver is using the same name macro,
pr_debug log statements are appearing in kmsg.
Fix this by moving the code under DEBUG to WLAN_DEBUG and
remove DEBUG macro from Kbuild.
Change-Id: I5bb385f91f9b6ba15629a5878625fefc21d4a7e1
CRs-Fixed: 1003261