defconfig: msm: Enable devmem support for sdm670

Enable devmem support in sdm670 debug builds also,
Official VTS testing uses performance builds, so this change
is not necessary.  And it negatively impacts some testing
teams.

Change-Id: I244b0273de718ec294161dfba72a49bcd97a474e
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>