defconfig: arm64: enable SSBD config for Kona v2

Kona v2 devices support speculative store bypass safe bit. Enable
the config to apply the mitigation for spectre variant 4.

Change-Id: I86d2b10049628af4637f21261bcf37d7bdc711be
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>