kernel.bbclass: Use lzma not lzmash for decompressing

kernel.bbclass: Use lzma not lzmash for decompressing

If kernel_do_compile() encounters a .lzma image for the initramfs, it
attempts to decompress it using the little-known "lzmash" utility.  This
may not be present, which will cause the build to fail.

Fortunately, it appears that the more mainstream "lzma" tool is
compatible so we can use that one instead.

(From OE-Core rev: f7a04cbdee67675ff6a8787709f3a312dc25bfec)

Signed-off-by: Phil Blundell <philb@gnu.org>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>