Unused files removed ...

Files "modules.builtin" probably have been copied from kernel tree.
This files not used by barebox and can be removed safely.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

add kernel gunzip implementation ...

The kernel uncompression functions have a unified API so use this
implementation to get it.

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