staging: nvec: Rewrite the interrupt handler

Rewrite the interrupt handler to use a state machine similar to
that found in the various kernels for the Advent Vega. This also
changes the code to use the new functions introduced in the
previous commits.

This also merges the rewrite sent in August 2011 by Marc
Dietrich, and thus also includes code by him. His original
patch can be found on the mailing list.

Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Acked-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>