decompressors: Use malloc/free wrappers ...

The decompressors are used both in a regular image and also for image
decompression. Both need different malloc implementations. Using
malloc/free directly in the decompressor code easily leads to include
file conflicts, so use MALLOC/FREE which can be defined correctly for
the two different usecases.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

lib: decompress_xz: fix function header to match prototype ...

Fixes:
lib/uncompress.c:124:10: warning: assignment from incompatible pointer type

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Add xz decompression support ...

This adds xz decompression support from the kernel. Both compressing
the barebox binary with xz and decompressing xz files on the commandline
is supported.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>