rcar-bsp: layer: Update BSP version to v4.15.0
rcar-bsp: layer: Update BSP version to v4.15.0

Update Yocto version to 4.15.0.

Signed-off-by: Duy Dang <2f6c7e7e2bec44da13d878c782ffd193b3d5aae2@renesas.com>

renesas-rcar/meta-renesas,renesas-rcar/meta-renesas,renesas-rcar/meta-renesas,renesas-rcar/meta-renesas