docs/interop/firmware.json: add new enum FirmwareFormat

Only a small subset of all blockdev drivers make sense for firmware
images. Introduce and use a new enum to represent this.

This also reduces the dependency on firmware.json from the global qapi
definitions.

Claim "Since: 3.0" for the new enum, because that's correct for its
members, and the members are what matters in the interface.

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240719-qapi-firmware-json-v6-1-c2e3de390b58@linutronix.de>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

docs/interop/firmware.json

@@ -15,7 +15,6 @@
 ##
 
 { 'include' : 'machine.json' }
-{ 'include' : 'block-core.json' }
 
 ##
 # @FirmwareOSInterface:
@@ -200,6 +199,20 @@
              'enrolled-keys', 'requires-smm', 'secure-boot',
              'verbose-dynamic', 'verbose-static' ] }
 
+##
+# @FirmwareFormat:
+#
+# Formats that are supported for firmware images.
+#
+# @raw: Raw disk image format.
+#
+# @qcow2: The QCOW2 image format.
+#
+# Since: 3.0
+##
+{ 'enum': 'FirmwareFormat',
+  'data': [ 'raw', 'qcow2' ] }
+
 ##
 # @FirmwareFlashFile:
 #
@@ -219,7 +232,7 @@
 ##
 { 'struct' : 'FirmwareFlashFile',
   'data'   : { 'filename' : 'str',
-               'format'   : 'BlockdevDriver' } }
+               'format'   : 'FirmwareFormat' } }
 
 
 ##