ACPI: Replace irqdomain.h include with struct declarations

linux/acpi.h includes irqdomain.h which includes of.h. Break the include
chain by replacing the irqdomain include with forward declarations for
struct irq_domain and irq_domain_ops which is sufficient for acpi.h.

of.h also includes mod_devicetable.h which many drivers implicitly
depend on. As acpi.h already includes it, just move it out of the
'#ifdef CONFIG_ACPI'.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>