This patch adds support for decompressing kernel binaries inside the FIT
image with LZMA or LZ4. This is only really needed for ARM64 (since the
other archs we currently support have built-in decompressors), so it's
only added there for now, although it could in theory work for all FIT
image architectures.

Also shuffled some code around and restructured some interfaces where it
seemed to make sense to make things simpler or cleaner.

CQ-DEPEND=CL:282743
BRANCH=smaug
BUG=chrome-os-partner:32184
TEST=Booted Oak with and without the kernel ebuild change. Booted Jerry.

Change-Id: Ifb013b5e7b3aa25ce9d37e116daeaeabd9da7558
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/281805