tests/qtest/readconfig-test: Check for the availability of USB controllers

The USB controllers might not be available in the QEMU binary
(e.g. when using the "--without-default-devices" configure switch),
so we have to check whether the devices can be used before running
the related test.

Message-Id: <20230512124033.502654-12-thuth@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/readconfig-test.c

@@ -207,7 +207,10 @@ int main(int argc, char *argv[])
     if (g_str_equal(arch, "i386") ||
         g_str_equal(arch, "x86_64")) {
         qtest_add_func("readconfig/x86/memdev", test_x86_memdev);
-        qtest_add_func("readconfig/x86/ich9-ehci-uhci", test_docs_config_ich9);
+        if (qtest_has_device("ich9-usb-ehci1") &&
+            qtest_has_device("ich9-usb-uhci1")) {
+            qtest_add_func("readconfig/x86/ich9-ehci-uhci", test_docs_config_ich9);
+        }
     }
 #if defined(CONFIG_SPICE) && !defined(__FreeBSD__)
     qtest_add_func("readconfig/spice", test_spice);