ls1046ardb: Add support power initialization

Add the chip power supply voltage initialization on LS1046ARDB.
Add function power_init_board(), and it will initialize the
PMIC and call the chip power initialization function.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>