PM / devfreq: Add tracepoint for frequency changes

Add a tracepoint for frequency changes of devfreq devices and
use it.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
[cw00.choi: Move print position of tracepoint and add more information]
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

trace: events: devfreq: Use fixed indentation size to improve readability

Each tracepoint infromation consist of the different size value.
So, in order to improve the readability, use the fixed indentation size.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

trace: events: add devfreq trace event file

The patch adds a new file for with trace events for devfreq
framework. They are used for performance analysis of the framework.
It also contains updates in MAINTAINERS file adding new entry for
devfreq maintainers.

Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>