Move PWR related init from bl2 to bl32.

Change-Id: I61b62ef2208bee0e502dd5fab277d806c205e7b1
Signed-off-by: Pascal Paillet <p.paillet@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/183647


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>
Tested-by: Yann GAUTIER <yann.gautier@st.com>