pwm: Enable compile testing for some of drivers

Some of the PWM drivers can be compile tested to increase build
coverage.

The Meson PWM driver requires COMMON_CLK dependency.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com> # For Broadcoam
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com> # For Meson
Acked-by: Claudiu Beznea <claudiu.beznea@microchip.com> # For Atmel
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>