PM / devfreq: rk3399_dmc: Use bitfield macro definitions for ODT_PD

We're going to add new usages, and it's cleaner to work with macros
instead of comments and magic numbers.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>