defconfig: msm: Enable PPTP support

mtpd will try to use OL2TP protocol (upstream) by default.
And the old protocol (OLAC) usage would be deprecated. Enable
PPTP support in kernel to provide VPN functionality.

CRs-Fixed: 2418285
Change-Id: Ia1d7eb97202c6fd7b98557b1b21f53096ba9cc44
Signed-off-by: Devi Sandeep Endluri V V <dendluri@codeaurora.org>