default or selected kernelversion does not have config value CONFIG_BACKLIGHT_ATMEL_PWM.
Result is shown for kernelversion 3.9.9

Atmel PWM backlight control

modulename: atmel-pwm-bl.ko

Linux Kernel Configuration
└─> Device Drivers
└─> Graphics support
└─> Backlight & LCD device support
└─> Atmel PWM backlight control

Say Y here if you want to use the PWM peripheral in Atmel AT91 and
AVR32 devices. This driver will need additional platform data to know
which PWM instance to use and how to configure it.

To compile this driver as a module, choose M here: the module will be
called atmel-pwm-bl.

source code: