boards/rp2040: support reboot bootloader via reset_usb_boot()

Add reset_usb_boot ROM function typedef and wire it into
board_reset() so that 'nsh> reboot bootloader'
(BOARDIOC_SOFTRESETCAUSE_ENTER_BOOTLOADER) on RP2040 boards enters
BOOTSEL USB mass-storage mode directly, matching the behavior
already available on rp23xx boards.  All other status values keep
the existing up_systemreset() behavior.

This affects all boards under boards/arm/rp2040/common (pico,
pico-w, feather-rp2040, xiao-rp2040, w5500-evb-pico, etc.) since
the change is in the shared board_reset() implementation.

Assisted-by: GitHubCopilot:claude-4.6-opus
Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

Author: JianyuWang0623

arch/arm/src/rp2040/rp2040_rom.h

@@ -63,3 +63,5 @@
  ****************************************************************************/
 
 typedef void *(*rom_table_lookup_fn)(uint16_t *table, uint32_t code);
+typedef void (*rom_reset_usb_boot_fn)(uint32_t usb_activity_gpio_pin_mask,
+                                      uint32_t disable_interface_mask);

boards/arm/rp2040/common/src/rp2040_reset.c

@@ -28,6 +28,10 @@
 #include <nuttx/board.h>
 #include <nuttx/arch.h>
 
+#include <sys/boardctl.h>
+
+#include "rp2040_rom.h"
+
 #ifdef CONFIG_BOARDCTL_RESET
 
 /****************************************************************************
@@ -56,7 +60,18 @@
 
 int board_reset(int status)
 {
-  up_systemreset();
+  if (status == BOARDIOC_SOFTRESETCAUSE_ENTER_BOOTLOADER)
+    {
+      rom_reset_usb_boot_fn reset_usb_boot;
+
+      reset_usb_boot = (rom_reset_usb_boot_fn)ROM_LOOKUP(ROM_RESET_USB_BOOT);
+      reset_usb_boot(0, 0);
+    }
+  else
+    {
+      up_systemreset();
+    }
+
   return 0;
 }