CPUs don't have drivers. Drivers are for devices attached to the computer,
like printers. The CPU is the core of the computer system.
All architectures work without proprietary software in principle. It's the
implementation that makes the difference. For example, Intel's processors are
distributed in such a way that proprietary software is required to use
them.[1] But there's nothing principally wrong, in a freedom sense, with x86
as an architecture.
Out of the three you mentioned, ARM is generally best when talking about new
processors, but ARM processors distributed today are not without problems.
The main problem with ARM stuff is it's usually distributed in a
System-on-a-Chip (SoC), and inextricably bundled with various components
(like a GPU and wireless adapter) that require proprietary software. This
isn't as bad as what e.g. Intel does with Intel ME, at least in my opinion,
but it's still a problem you tend to face.
