defconfig: disable DDR Health Monitor feature from perf defconfig on 8994

DDR Health Monitor feature is required to be enabled only on non-perf
configs to avoid security risk. Disable this feature on perf defconfig for
8994.

Change-Id: Idc61764acfc9b744493cb343b8dc460fc2e3ae81
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>