build: use logger.isEnabledFor, not getEffectiveLevel

build: use logger.isEnabledFor, not getEffectiveLevel

I think this is less confusing, and avoids needing to know about the *range*
of logging levels, instead simply asking what we really want to know.

(Bitbake rev: dc2264387617586b5c0a61e126c75edde5e7abcd)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>