Use constants for VBlank handlers

mobile/mobile_40.asm

@@ -94,6 +94,7 @@ DisableMobile:
 	xor a
 	ldh [hMobileReceive], a
 	ldh [hMobile], a
+	assert VBLANK_NORMAL == 0
 	xor a
 	ldh [hVBlank], a
 	call NormalSpeed
@@ -1378,7 +1379,7 @@ Function1008e0:
 	push bc
 	xor a
 	ldh [hBGMapMode], a
-	ld a, $03
+	ld a, VBLANK_CUTSCENE_CGB
 	ldh [hVBlank], a
 	call Function100970
 	call Function100902