yasm: add from meta-oe and tweak

yasm: add from meta-oe and tweak

This is needed for x264. Enabling it for libav also improves performance
on x86 and x86-64. Two minor changes from the meta-oe recipe:

* Set SUMMARY instead of DESCRIPTION
* Drop setting of S - it was setting it to the same as the default

(From OE-Core rev: 2619c81d6641ef5d4dee58c128a1af140429c248)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>