lib: adjust new experimental pro-controller mappings

The pro-controller patches are on their way into linux-3.11 and we changed
the mappings again to comply with the new gamepad rules.

Add few #ifdefs for all those who still compile this with older kernel
headers.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiishow: show MP status

We now write M+ if MP is connected and available.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiibind: pass argument to "read"

On some machines, "read" actually requires a variable name to read data
into. Hence, pass a temporary variable so xwiibind.sh works on these
machines.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
xwiibind: extend configurability

Allow users to specify binary paths/prefix on the command line and
correctly check whether the given files are available via `which`. This
allows users to use this tool without modifying the source code.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>