docs: raspberrypi: Avoid abbreviating to RPi

Prefer to use more descriptive terms.

Signed-off-by: Andrew Featherstone <[email protected]>

Author: ajf58

tests/drivers/gpio/gpio_api_1pin/boards/pico_plus2_rp2350b_m33.overlay

@@ -4,5 +4,5 @@
  * Copyright (c) 2024 TOKITA Hiroshi
  */
 
-/* Pico Plus2 is pin-compatible with the RPi-Pico2, so reuse. */
+/* Pico Plus2 is pin-compatible with the Raspberry Pi Pico 2, so reuse. */
 #include "rpi_pico2_rp2350a_m33.overlay"

tests/drivers/gpio/gpio_basic_api/boards/pico_plus2_rp2350b_m33.overlay

@@ -4,5 +4,5 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-/* Pico Plus2 is pin-compatible with the RPi-Pico, so reuse. */
+/* Pico Plus2 is pin-compatible with the Raspberry Pi Pico, so reuse. */
 #include "rpi_pico.overlay"