defconfig: mdm9630: Enable WCNSS pre-alloc

WLAN driver will use this pre-allocated memory (when available)
for large memory allocations; this will prevent WLAN driver load
failures because of the un-availability of the large size slabs
during module load

Change-Id: Ic210c09a3d3e64bc31fdd141183caa4bc56e553a
Signed-off-by: Prashanth Bhatta <bhattap@codeaurora.org>