genirq: Add an accessor for IRQ_PER_CPU flag

This patch adds an accessor function for IRQ_PER_CPU flag.
The accessor function is useful to determine whether an IRQ is percpu or not.

This patch is based on an older patch posted by Chris Smith here [1].
There is a minor change w.r.t. Chris's original patch: The accessor function
is renamed as 'irq_is_percpu' instead of 'irq_is_per_cpu'.

[1]: http://lkml.indiana.edu/hypermail/linux/kernel/1207.3/02955.html



Signed-off-by: Chris Smith <chris.smith@st.com>
Signed-off-by: Vinayak Kale <vkale@apm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Git-commit: 7f4a8e7b1943c1fc7e4b08509e308197babdcd5b
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[imaund@codeaurora.org: we picked the implementation of irq_is_percpu
  from a patch, where the API was named irq_is_per_cpu. This change
  duplicates the implementation as irq_is_percpu and irq_is_per_cpu,
  until users of this API can be updated to irq_is_percpu. At that
  point, irq_is_per_cpu will be removed.]
Change-Id: I4536b614534c7d496f985480458b356c5938f2ea
Signed-off-by: Ian Maund <imaund@codeaurora.org>