Fix PSP build issues

src/display/CMakeLists.txt

@@ -33,6 +33,8 @@ elseif(DUSK_TARGET_SYSTEM STREQUAL "psp")
       DISPLAY_SDL2=1
       DISPLAY_WINDOW_WIDTH_DEFAULT=480
       DISPLAY_WINDOW_HEIGHT_DEFAULT=272
+      DISPLAY_WIDTH=480
+      DISPLAY_HEIGHT=272
       DISPLAY_SIZE_DYNAMIC=0
   )
 endif()

src/display/displaydefs.h

@@ -21,6 +21,15 @@
   #error "Need to specify display backend."
 #endif
 
+#if DISPLAY_SIZE_DYNAMIC == 0
+  #ifndef DISPLAY_WIDTH
+    #error "DISPLAY_WIDTH must be defined when DISPLAY_SIZE_DYNAMIC is 0."
+  #endif
+  #ifndef DISPLAY_HEIGHT
+    #error "DISPLAY_HEIGHT must be defined when DISPLAY_SIZE_DYNAMIC is 0."
+  #endif
+#endif
+
 #ifndef DISPLAY_WINDOW_WIDTH_DEFAULT
   #error "DISPLAY_WINDOW_WIDTH_DEFAULT must be defined."
 #endif