platform-msi: Prepare for real per device domains

platform-msi: Prepare for real per device domains

Provide functions to create and remove per device MSI domains which replace
the platform-MSI domains. The new model is that each of the devices which
utilize platform-MSI gets now its private MSI domain which is "customized"
in size and with a device specific function to write the MSI message into
the device.

This is the same functionality as platform-MSI but it avoids all the down
sides of platform MSI, i.e. the extra ID book keeping, the special data
structure in the msi descriptor. Further the domains are only created when
the devices are really in use, so the burden is on the usage and not on the
infrastructure.

Fill in the domain template and provide two functions to init/allocate and
remove a per device MSI domain.

Until all users and parent domain providers are converted, the init/alloc
function invokes the original platform-MSI code when the irqdomain which is
associated to the device does not provide MSI parent functionality yet.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240127161753.114685-6-apatel@ventanamicro.com