defconfig: arm64: Add misc_debug_defconfig for memory and fuzzing tests

Add misc_debug_defconfig which can be used for generating kasan/kcov
enabled builds by merging this config using merge_config.sh script
with other target defconfigs during build generation.

Change-Id: I4469d08ecb47bdaabd9aef9f894208f83ca2d757
Signed-off-by: Sridhar Parasuram <sridhar@codeaurora.org>