samples: drivers: led: pwm: Add rpi_pico2 board

The RP2350's PWM peripheral is largely unchanged from the RP2040's, but
the higher clock frequency means the long blink delay must be lower.

(cherry picked from commit 6a47f72)

Original-Signed-off-by: Andrew Featherstone <andrew.featherstone@gmail.com>
GitOrigin-RevId: 6a47f72
Cr-Build-Id: 8727676392421021649
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8727676392421021649
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: Ic3a851b4a6683145b39bf4ec15a9da9113c63cf4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6121903
Reviewed-by: Ting Shen <phoenixshen@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Commit-Queue: Ting Shen <phoenixshen@chromium.org>

samples/drivers/led/pwm/boards/rpi_pico2_rp2350a_m33.conf

@@ -0,0 +1,3 @@
+CONFIG_BLINK_DELAY_SHORT=20
+CONFIG_BLINK_DELAY_LONG=50
+CONFIG_FADE_DELAY=15

samples/drivers/led/pwm/boards/rpi_pico2_rp2350a_m33.overlay

@@ -0,0 +1,8 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2024 Andrew Featherstone <andrew.featherstone@gmail.com>
+ */
+
+/* Pico 2 is compatible with the Pico 1, so reuse. */
+#include "rpi_pico.overlay"