In the commit title: the description should be some sort of action,
describing what the commit does. Using "should" doesn't make it clear
the commit actually does that.

This is not simply a matter of consistency: without using
user_uintptr_t, we cannot propagate capabilities in PCuABI. Because at
least one proc_ioctl handler (cache_ioctl_procfs) expects the argument
to be a pointer, we need to change the callback signature (otherwise we
would have been better off not changing it).

 We have avoided doing that for other compat ioctl callbacks, including
the main file_operations one, because it is semantically incorrect: in
compat(64), the argument really is just an unsigned long.

Instead of changing this callback signature, it would be better to fix
the existing code that sets a proc_compat_ioctl callback. AFAICT we only
need to fix proc_bus_pci_ops, and we can do it in the same way as
esas2r_proc_ops, i.e. by using the compat_*_ioctl helpers.
proc_bus_pci_ioctl() does not expect a pointer, so we should use the
compat_noptr_ioctl helper there. See [1] for more information.