dt-bindings: pwm: at91: Add SAMA7G5 compatible strings list

Add compatible strings list for SAMA7G5.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>