qemu*: restrict NFSD to linux-yocto only

qemu*: restrict NFSD to linux-yocto only

In the current releases, not all linux-yocto derived kernels have NFS
support, or NFS support fragments availble. To ensure that derived
kernels like linux-yocto-cutom continue to work against poky-lsb,
we can make the KERNEL_FEATURE append more specific to the linux-yocto
recipe.

(From OE-Core rev: 799f53e8844748a930a9cbc7a4cf1056f19bb037)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>