Enable perf in obmc-phosphor-debugtools

This enables the userspace 'perf' tool and the corresponding kernel
configuration.

PERF_EVENTS is enabled on ast2500. It was already enabled on ast2400.

TIMER_STATS is enabled. This has low runtime impact when not enabled. It
defaults to off.

Change-Id: Iac1761aec999679b611e9bf9b51d0fe585d7ac5c
Signed-off-by: Joel Stanley <joel@jms.id.au>
2 files changed