Expose drive_add on all architectures

All architectures can now use drive_add on the monitor. This of course
does not mean that there is hotplug support for the specific platform,
so in order to actually make use of the new drives you still need to
have a hotplug capable device.
Signed-off-by: NAlexander Graf <agraf@suse.de>

hmp-commands.hx

@@ -846,7 +846,6 @@ STEXI
 Snapshot device, using snapshot file as target if provided
 ETEXI
 
-#if defined(TARGET_I386)
     {
         .name       = "drive_add",
         .args_type  = "pci_addr:s,opts:s",
@@ -859,7 +858,6 @@ ETEXI
         .help       = "add drive to PCI storage controller",
         .mhandler.cmd = drive_hot_add,
     },
-#endif
 
 STEXI
 @item drive_add