sdm845 defconfig: Enable PPP related defconfigs

Enabled PPP related configs for VPN functionality
to work on sdm845.

CRs-Fixed: 2019475
Change-Id: Ib8d0a98ef4219f2ab33008a4da3e93f22e85f538
Signed-off-by: Devi Sandeep Endluri V V <dendluri@codeaurora.org>
Signed-off-by: Tejaswi Tanikella <tejaswit@codeaurora.org>