the life is much simpler if copy_regset_to_user() (and ->get())
gets called only with pos == 0; sparc32 PTRACE_GETREGS and
PTRACE_GETFPREGS are among the few things that use it to fetch
pieces of regset _not_ starting at the beginning.  It's actually
easier to define a separate regset that would provide what
we need, rather than trying to cobble that from the one
PTRACE_GETREGSET uses.

Extra ->get() instances do not amount to much code and once
we get the conversion of ->get() to new API (dependent upon the
lack of weird callers of ->get()) they'll shrink a lot, along
with the rest of ->get() instances...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>