qapi: Extract PCI commands to 'pci.json'

Only qemu-system-FOO and qemu-storage-daemon provide QMP
monitors, therefore such declarations and definitions are
irrelevant for user-mode emulation.

Extracting the PCI commands to their own schema reduces the size of
the qapi-misc* headers generated, and pulls less QAPI-generated code
into user-mode.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200913195348.1064154-9-philmd@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index f99b5db..be0a8e6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1617,6 +1617,7 @@
 F: hw/misc/pci-testdev.c
 F: hw/pci/*
 F: hw/pci-bridge/*
+F: qapi/pci.json
 F: docs/pci*
 F: docs/specs/*pci*
 F: default-configs/pci.mak