shpc: disallow unplug when power indicator is blinking

Pressing attention button has special meaning when power indicator is
blinking. Better just not do it.

For example, trying to remove device immediately after hotplug leads to
both commands succeded but device not actually unrealized.

Same thing for PCIE hotplug was done in
  81124b3c7a "pcie: add power indicator blink check"

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Message-Id: <20221116214458.82090-1-vsementsov@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci/shpc.c

@@ -568,6 +568,13 @@ void shpc_device_unplug_request_cb(HotplugHandler *hotplug_dev,
 
     state = shpc_get_status(shpc, slot, SHPC_SLOT_STATE_MASK);
     led = shpc_get_status(shpc, slot, SHPC_SLOT_PWR_LED_MASK);
+
+    if (led == SHPC_LED_BLINK) {
+        error_setg(errp, "Hot-unplug failed: "
+                   "guest is busy (power indicator blinking)");
+        return;
+    }
+
     if (state == SHPC_STATE_DISABLED && led == SHPC_LED_OFF) {
         shpc_free_devices_in_slot(shpc, slot);
         shpc_set_status(shpc, slot, 1, SHPC_SLOT_STATUS_MRL_OPEN);