The current SAMv7 PWM driver assumes that all PWM channels should work in sync mode, but that is a partial case of a generic PWM driver operation. Start SAMv7 PWM channels in async mode. The sync mode should be implemeted either using ioctl command or via a separate Kconfig option. Signed-off-by: Petro Karashchenko <petro.karashchenko@gmail.com>