[MIPS] JMR3927 fixes.

 o Check if IRQ is disabled or in progress before reenabling interrupts
   in jmr3927_irq_end..
 o s/spinlock_irqsave/spin_lock_irqsave/
 o s/spinlock_irqrestore/spin_unlock_irqrestore/
 o Flush write buffer after setting IRQ mask
 o In 2.6 jmr3927_ioc_interrupt interrupt handlers return irqreturn_t

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>