kconfig check: require DEVPTS_MULTIPLE_INSTANCES (MR 2051)

Check for CONFIG_DEVPTS_MULTIPLE_INSTANCES, as it's required by bwrap
and therefore flatpak and epiphany.

See pmaports!2145

pmb/config/__init__.py

@@ -263,6 +263,11 @@ necessary_kconfig_options = {
             "USER_NS": True,
         },
     },
+    "<4.7.0": {
+        "all": {
+            "DEVPTS_MULTIPLE_INSTANCES": True,
+        }
+    },
     "<5.2.0": {
         "armhf armv7 x86": {
             "LBDAF": True