The hard work of parsing fields per-CPU, handling heterogeneous
features, and excluding features from userspace is already done by
update_special_regs. We can build our set of HWCAPs from the result.
This also exposed a small bug in update_special_regs, in which the
generated bitmask was not wide enough, and as a result some bits
weren't being exposed in user_cpu_desc.
While here, adjust some formatting.