refactor NILRT_RELEASE_NAME as NILRT_FEED_NAME
refactor NILRT_RELEASE_NAME as NILRT_FEED_NAME

The NILRT_RELEASE_NAME variable is intimately tied to the opkg
base-feeds URIs, Since we're about to add an 'unstable' feed, it might
be confusing to keep calling the variable `_RELEASE_NAME`.

Instead, refactor it to `NILRT_FEED_NAME`.

Signed-off-by: Alex Stewart <04cdb2793e4fb0120cc30d1c823099f3862701f4@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt