xtensa: convert to asm-generic/hardirq.h

Also remove lots of unused irq_cpustat fields.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>