ARM: multi_v7_defconfig: Select PWM_RCAR as module

Enable PWM support for R-Car and friends by default.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>