MIPS: Octeon: Simplify irq_cpu_on/offline irq chip functions

Make use of the IRQCHIP_ONOFFLINE_ENABLED flag and remove the
wrappers. Use irqd_irq_disabled() instead of desc->status, which will
go away.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: David Daney <ddaney@caviumnetworks.com>