ARM: 6806/1: irq: introduce entry and exit functions for chained handlers

Some chained IRQ handlers are written to cope with primary chips of
potentially different flow types. Whether this a sensible thing to do
is a point of contention.

This patch introduces entry/exit functions for chained handlers which
infer the flow type of the primary chip as fasteoi or level-type by
checking whether or not the ->irq_eoi function pointer is present and
calling back to the primary chip as necessary. Other methods of flow
control are not considered.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>