tools/squashfs: rename to squashfs3-lzma

tools/squashfs: rename to squashfs3-lzma

The name of squashfs is confusing since in reality it's a really old
version using an old lzma library. This tools is used for old ath79
netgear target and to produde a fake squasfs3 image needed for some
specific bootloader from some OEM (AVM for example)

Rename squashfs tool to squasfs3-lzma to better describe it.
Rename the installed bin from mksquashfs-lzma to mksquashfs3-lzma.
Use tar transform to migrate the root directory in tar to the new
naming.
Drop redundant PKG_CAT variable not needed anymore.
Also update any user of this tool.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>