ANDROID: gki_defconfig: x86: Enable KERNEL_LZ4

Compress the kernel with lz4 instead of gzip. On x86 this must be
controlled explicitly by kbuild, as decompressor code is prepended
to the compressed kernel artifact.

On arm64 this option is not needed as "make Image.lz4" can be used
instead, or the Image can be compressed in a separate step.

Bug: 150391496
Change-Id: I2d0ce7f937f2a952b4310f53c8b03dc8d721b050
Signed-off-by: Alistair Delva <adelva@google.com>