defconfig: msm: Enable KPTI on sdmsteppe, trinket

Enable KPTI mitigation on sdmsteppe, trinket since
it is needed as part of android CTS. The mitigation
is to unmap kernel when running in userspace.

Change-Id: I95fc36f64811ffc2720ea1d64b59ace179192124
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>