libyaml: Enable static lib on native/nativesdk

Helps building static tools which depend on libyaml during build or
shipped with SDK

libyaml is MIT licensed so static linking would not be as prohibitive

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>