Now that entry code handles IRQ entry (including setting the IRQ regs)
before calling irqchip code, irqchip code can safely call
generic_handle_domain_irq(), and there's no functional reason for it to
call handle_domain_irq().

Let's cement this split of responsibility and remove handle_domain_irq()
entirely, updating irqchip drivers to call generic_handle_domain_irq().

For consistency, handle_domain_nmi() is similarly removed and replaced
with a generic_handle_domain_nmi() function which also does not perform
any entry logic.

Previously handle_domain_{irq,nmi}() had a WARN_ON() which would fire
when they were called in an inappropriate context. So that we can
identify similar issues going forward, similar WARN_ON_ONCE() logic is
added to the generic_handle_*() functions, and comments are updated for
clarity and consistency.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>