spl: spl_legacy: Add lzma decompression support for legacy image

spl: spl_legacy: Add lzma decompression support for legacy image

This patch adds support for decompressing LZMA compressed u-boot payload
in legacy uImage format.

Using this patch together with u-boot-lzma.img may be useful for some
platforms as they can reduce the size and load time of u-boot payload.

Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>
Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>