patman: Correct lz4 compression parameters

At present on large files, lz4 uses a larger block size (e.g. 256KB) than
the 64KB supported by the U-Boot decompression implementation. Also it is
optimised for maximum compression speed, producing larger output than we
would like.

Update the parameters to correct these problems.

Signed-off-by: Simon Glass <sjg@chromium.org>