When SPDX manifests are enabled for OE-Core, it hightlights that the SDK_NAME
default isn't working well. Add IMAGE_BASENAME to it to help avoid conflicts
between outut files.
I suspect the defaults aren't working well and most distros are already
overriding this.
(From OE-Core rev: fba8fc22898f8455bd39f9a5f21ff056f2c0cd91)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>