stm32mp1: add general SYSCFG management

The system configuration controller is mainly used to manage
the compensation cell and other IOs and system related settings.

The SYSCFG driver is in charge of configuring masters on the interconnect,
IO compensation, low voltage boards, or pull-ups for boot pins.
All other configurations should be handled in Linux drivers requiring it.

Device tree files are also updated to manage vdd-supply regulator.

Change-Id: I10fb513761a7d1f2b7afedca9c723ad9d1bccf42
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>