popn: boot with 3 monitors (#636)

## Link to GitHub Issue or related Pull Request, if one exists
#618 

## Description of change
Take the monitor hooks added for IIDX/SDVX #612 and apply it to popn as
well now that popn has a subscreen.

There is a debug option in game that actually uses three monitors, which
can be activated via hex edits. This will prevent that from working.

## Testing
Tested with 3 monitors, fs and windowed.

src/spice2x/games/popn/popn.cpp

@@ -232,6 +232,7 @@ namespace games::popn {
                             // TODO: is this what the game expects for subscreen?
                             // TODO: what if there are 3+ monitors?
                             targetName->outputTechnology = DISPLAYCONFIG_OUTPUT_TECHNOLOGY_HDMI;
+                            targetName->connectorInstance = 0;
                         }
                         break;
                     }
@@ -634,6 +635,8 @@ namespace games::popn {
             wintouchemu::hook_title_ends("", "Main Screen", avs::game::DLL_INSTANCE);
         }
 
+        sysutils::hook_EnumDisplayDevicesA();
+
 #endif
 
     }