Don't use create_proc_read_entry() as that is deprecated, but rather use
proc_create_data() and seq_file instead.  Whilst we're at it, reduce the
number of show functions where we can share them.

Question: Do any of the registers read by proc_get_registers() have side
effects upon reading?  If so, locking will be required.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: Maxim Mikityanskiy <maxtram95@gmail.com>
cc: YAMANE Toshiaki <yamanetoshi@gmail.com>
cc: Bill Pemberton <wfp5p@virginia.edu>
cc: Andrea Merello <andreamrl@tiscali.it>
cc: linux-wireless@vger.kernel.org
cc: devel@driverdev.osuosl.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>