Moving to ARM from 8 bit AVR - how to take the 1st step?
No one forces you to use a peripheral library (ASF), you may very well code directly by toggling bits pretty much like on AVRs.  The ASF probably includes a file which contains all the registers' definitions so that you can code manually if you want to.

I also found that the peripheral library (for STM32, though) was not easy to use when I started, but once you understand how it works, you no longer need to care about low level idiosyncrasies of your device, so that your code is more portable and faster to develop.  I must admit that I prefer to code directly with registers, but there is a reason why ARM provide a kind of standard (CMSIS) for peripheral libraries and it is for ease of use: once you know an ARM, you know most of them, because the peripheral library wraps most differences behind a layer of abstraction.  You are better off taking a not-so-steep learning curve with the peripheral library provided for your chip (there are tons of examples on the Internet using peripheral libraries) than using register configuration, because you will end up with very few examples on the Internet.

Start with a small project and then try using peripherals using the library.  If you really want not to use it, then you probably will be on your own, but still, you can look in the ASF to see how they implemented stuff and reinvent the wheel if you want to.  Your call.