arm64: defconfig: Enable BD9571MWV regulator

The BD9571 PMIC is present on the Renesas Salvator-X(S) and R-Car
Starter Kit Premier/Pro development boards.

Signed-off-by: Dien Pham <dien.pham.ry@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>