tests: stub dma_gpu_ll_cycles_to_event in the ram-map fixture

psx_ram_runtime_map_test links dma.c without dma_gpu_ll.c. The linked-list
kick now asks for the walk's next event while it holds the CPU, so the
fixture needs that symbol too. The stubbed start leaves the walk inactive,
so the hold never loops here.

runtime/tests/psx_ram_runtime_map_stubs.c

@@ -91,6 +91,9 @@ void cdrom_debug_snapshot(void *out) { (void)out; }
 uint32_t cdrom_dma_sector_word_count(void) { return 0; }
 void dma_gpu_ll_start(void *s, uint32_t a, uint32_t m) { (void)s; (void)a; (void)m; }
 void dma_gpu_ll_cancel(void *s) { (void)s; }
+/* The kick's CPU hold asks for the next walk event; the stubbed start leaves
+ * the walk inactive, so the hold never loops. */
+uint32_t dma_gpu_ll_cycles_to_event(const void *s) { (void)s; return 0xFFFFFFFFu; }
 void gpu_ws_begin_linked_list(void) {}
 void gpu_ws_end_linked_list(void) {}
 void gpu_ws_prepass_linked_list(uint32_t a) { (void)a; }