platform-msi: Make platform_msi_create_device_domain() ACPI aware

The irqdomain creation that is carried out in:

platform_msi_create_device_domain()

relies on the fwnode_handle interrupt controller token to associate the
interrupt controller with a specific irqdomain. Current code relies on
the OF layer to retrieve a fwnode_handle for the device representing the
interrupt controller from its device->of_node pointer.  This makes
platform_msi_create_device_domain() DT specific whilst it really is not
because after the merge of commit f94277af ("of/platform: Initialise
dev->fwnode appropriately") the fwnode_handle can easily be retrieved
from the dev->fwnode pointer in a firmware agnostic way.

Update platform_msi_create_device_domain() to retrieve the interrupt
controller fwnode_handle from the dev->fwnode pointer so that it can
be used seamlessly in ACPI and DT systems.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Wei Xu <xuwei5@hisilicon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>