defconfig: sdx: Add new defconfig files for SDX hedgehog

Add initial sdx_defconfig and sdx-perf_defconfig for
sdxhedgehog.

CRs-Fixed: 1075136
Change-Id: I044a202f6b3ddd8726749e1e18438a63e1d81ffc
Signed-off-by: Runmin Wang <runminw@codeaurora.org>