gpio: mvebu: Fix check for pwm support on non-A8K platforms

pwm support incompatible with Armada 80x0/70x0 API is not only in
Armada 370, but also in Armada XP, 38x and 39x. So basically every non-A8K
platform. Fix check for pwm support appropriately.

Fixes: 85b7d8ab

 ("gpio: mvebu: add pwm support for Armada 8K/7K")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>