Accept USB BOOTSEL reboot on the UART firmware

The regular firmware now answers the EP0 vendor INFO and BOOTSEL reboot
requests with the AIO wire protocol, so switch-pico-config reboot bootsel
works when the Pico's USB side is on a PC. Wire constants move to
usb_management_protocol.h; other operations stall.

tests/native_stubs/pico/bootrom.h

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void reset_usb_boot(uint32_t usb_activity_gpio_pin_mask,
+                    uint32_t disable_interface_mask);
+
+#ifdef __cplusplus
+}
+#endif

tests/native_stubs/pico/time.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #ifdef __cplusplus
@@ -12,6 +13,8 @@ typedef struct {
 
 absolute_time_t get_absolute_time(void);
 uint32_t to_ms_since_boot(absolute_time_t time);
+absolute_time_t make_timeout_time_ms(uint32_t milliseconds);
+bool time_reached(absolute_time_t time);
 
 #ifdef __cplusplus
 }