PM / devfreq: Drop custom MIN/MAX macros

Drop the custom MIN/MAX macros in favour of the standard min/max from
kernel.h

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>