misc: Add hardware dependencies to Atmel drivers

According to the driver descriptions, the atmel_pwm and atmel-ssc
drivers are only useful on Atmel AT32 and AT91 systems. So add
hardware dependencies to these drivers to hide them on other systems.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>