feat(regulator): add a regulator framework

Add a regulator framework to:
- provide an interface to consumers and drivers,
- connect consumers with drivers,
- handle most of devicetree-parsing,
- handle always-on and boot-on regulators,
- handle min/max voltages,

Change-Id: I23c939fdef2c71a416c44c9de332f70db0d2aa53
Signed-off-by: Pascal Paillet <p.paillet@st.com>