lib: Mark lz4 as relocation code

lib: Mark lz4 as relocation code

Mark the lz4 decompression code as needed by relocation. This is used to
decompress the next-phase image.

Drop the 'safe' versions from SPL as they are not needed. Change the
static array to a local one, to avoid a crash errors when trying to
access the data from relocated code. Make this conditional to avoid a
code-size increase when SPL_RELOC is not used/

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