dt-bindings: ipmi: Add optional SerIRQ property to ASPEED KCS devices

Allocating IO and IRQ resources to LPC devices is in-theory an operation
for the host, however ASPEED don't appear to expose this capability
outside the BMC (e.g. SuperIO). Instead, we are left with BMC-internal
registers for managing these resources, so introduce a devicetree
property for KCS devices to describe SerIRQ properties.

Signed-off-by: Andrew Jeffery <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Corey Minyard <[e-mail]>

Documentation/devicetree/bindings/ipmi/aspeed,ast2400-kcs-bmc.yaml

···
       channels the status address is derived from the data address, but the
       status address may be optionally provided.
 
+  aspeed,lpc-interrupts:
+    $ref: "/schemas/types.yaml#/definitions/uint32-array"
+    minItems: 2
+    maxItems: 2
+    description: |
+      A 2-cell property expressing the LPC SerIRQ number and the interrupt
+      level/sense encoding (specified in the standard fashion).
+
+      Note that the generated interrupt is issued from the BMC to the host, and
+      thus the target interrupt controller is not captured by the BMC's
+      devicetree.
+
   kcs_chan:
     deprecated: true
     $ref: '/schemas/types.yaml#/definitions/uint32'
···
 
 examples:
   - |
+    #include <dt-bindings/interrupt-controller/irq.h>
     kcs3: kcs@24 {
         compatible = "aspeed,ast2600-kcs-bmc";
         reg = <0x24 0x1>, <0x30 0x1>, <0x3c 0x1>;
         aspeed,lpc-io-reg = <0xca2>;
+        aspeed,lpc-interrupts = <11 IRQ_TYPE_LEVEL_LOW>;
         interrupts = <8>;
     };