classes/populate_sdk_ext: require uninative

classes/populate_sdk_ext: require uninative

It seems that possibly due to OE-Core commit
ac59063bee0e32d0737340974f657341717a6abe, binaries produced without
uninative aren't compatible with the uninative glibc. I did try earlier
to ensure that the eSDK could work without uninative since the default
configuration in OE-Core does not enable it, but it seems like I didn't
go far enough. Given the practical considerations, just give up and
require uninative to be enabled in order to build the eSDK. I'm not
particularly happy about this, but I don't seem much of an alternative.

Fixes [YOCTO #10566].

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>