defconfig: msm: Enable CC_OPTIMZE_FOR_SIZE config for sdm845

While compiling kernel with LLVM, the size of the kernel image
exceeds the limit of bootloader. To optimize the size of the kernel
image, enable the CONFIG_CC_OPTIMIZE_FOR_SIZE for sdm845 debug and
perf defconfig.

Change-Id: If705f8f8bf436eab202fa77ad8a8a15a264d5224
Signed-off-by: Shadab Naseem <snaseem@codeaurora.org>