ARM: shmobile: defconfig: Enable PWM

RZ/G1 and R-Car platforms have PWM timers. This patch enables PWM support
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>