defconfig: Add defconfig for kdump capture kernel on gen3_auto

This is common defconfig used by sa8155, sa6155 and sa8195 SoCs for
capture kernel.

Change-Id: I30fc0f15497d5205bea5c6ff5e5b4aa1e2aadac3
Signed-off-by: Akshay Adiga <aadiga@codeaurora.org>