squashfs-tools: add PACKAGECONFIGs for all the tunables

squashfs-tools: add PACKAGECONFIGs for all the tunables

Upstream lets you control what compression algorithms are used, so add
PACKAGECONFIGs for them all.

Instead of bundling a copy of the SevenZIP SDK from 2009 (!), reuse XZ.  This
means we can drop Public Domain from the license list.

Also -e was removed from EXTRA_OEMAKE in 2016 (oe-core aeb653) so the fiddling
to work around that can be removed.

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>