arm64: defconfig: Enable Renesas MTU3a PWM config

Enable PWM config for Renesas MTU3a PWM as it is populated on
RZ/{G2L, LC, UL} and RZ/V2L SMARC EVKs.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230703132706.355237-1-biju.das.jz@bp.renesas.comSigned-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

arch/arm64/configs/defconfig

@@ -1345,6 +1345,7 @@ CONFIG_PWM_MEDIATEK=m
 CONFIG_PWM_RCAR=m
 CONFIG_PWM_RENESAS_TPU=m
 CONFIG_PWM_ROCKCHIP=y
+CONFIG_PWM_RZ_MTU3=m
 CONFIG_PWM_SAMSUNG=y
 CONFIG_PWM_SL28CPLD=m
 CONFIG_PWM_SUN4I=m