bitbake.conf: Add all layers (from BBLAYERS) to PSEUDO_IGNORE_PATHS

Instead of ignoring ${COREBASE}/meta in PSEUDO_IGNORE_PATHS (which may
or may not ignore all layers depending on how they are named and placed
under ${COREBASE}), ignore all layers.

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>