virt: vmgenid: add support for devicetree bindings

Extend the vmgenid platform driver to support devicetree bindings. With
this support, hypervisors can send vmgenid notifications to the virtual
machine without the need to enable ACPI. The bindings are located at:
Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml

Since this is no longer ACPI-dependent, remove the dependency from
Kconfig and protect the ACPI code with a single ifdef.

Signed-off-by: Sudan Landge <sudanl@amazon.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
Tested-by: Babis Chalios <bchalios@amazon.es>
[Jason: - Small style cleanups and refactoring.
        - Re-work ACPI conditionalization. ]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>