configs: Move CONFIG_PROVE_LOCKING from linaro-base.conf to debug.conf

configs: Move CONFIG_PROVE_LOCKING from linaro-base.conf to debug.conf

CONFIG_PROVE_LOCKING is an expensive option which adds significant
overhead to lock operations. The examples are 5% power consumption increase
for vexpress with this option enabled, and improving netperf on the loopback
results by ~200% after disabling DEBUG_MUTEXES (DEBUG_MUTEXES is selected by
PROVE_LOCKING).

Move CONFIG_PROVE_LOCKING to a separate debug.conf fragment, so that it
could be enabled only when it is needed.

Signed-off-by: Andrey Konovalov <andrey.konovalov@linaro.org>