Add board definition for Seeed Xiao RP2040 (earlephilhower#691)

* Add board definition for Seeed Xiao RP2040

https://www.seeedstudio.com/XIAO-RP2040-v1-0-p-5026.html
https://wiki.seeedstudio.com/XIAO-RP2040/

Author: ryanplusplus

src/boards/include/boards/seeed_xiao_rp2040.h

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// -----------------------------------------------------
+// NOTE: THIS HEADER IS ALSO INCLUDED BY ASSEMBLER SO
+//       SHOULD ONLY CONSIST OF PREPROCESSOR DIRECTIVES
+// -----------------------------------------------------
+
+#ifndef _BOARDS_SEEED_XIAO_RP2040_H
+#define _BOARDS_SEEED_XIAO_RP2040_H
+
+// For board detection
+#define SEEED_XIAO_RP2040
+
+// On some samples, the xosc can take longer to stabilize than is usual
+#ifndef PICO_XOSC_STARTUP_DELAY_MULTIPLIER
+#define PICO_XOSC_STARTUP_DELAY_MULTIPLIER 64
+#endif
+
+//------------- UART -------------//
+#ifndef PICO_DEFAULT_UART
+#define PICO_DEFAULT_UART 0
+#endif
+
+#ifndef PICO_DEFAULT_UART_TX_PIN
+#define PICO_DEFAULT_UART_TX_PIN 0
+#endif
+
+#ifndef PICO_DEFAULT_UART_RX_PIN
+#define PICO_DEFAULT_UART_RX_PIN 1
+#endif
+
+//------------- LED -------------//
+#ifndef PICO_DEFAULT_LED_PIN
+#define PICO_DEFAULT_LED_PIN 25
+#endif
+
+#ifndef PICO_DEFAULT_LED_PIN_INVERTED
+#define PICO_DEFAULT_LED_PIN_INVERTED 1
+#endif
+
+#ifndef PICO_DEFAULT_WS2812_PIN
+#define PICO_DEFAULT_WS2812_PIN 12
+#endif
+
+#ifndef PICO_DEFAULT_WS2812_POWER_PIN
+#define PICO_DEFAULT_WS2812_POWER_PIN 11
+#endif
+
+//------------- I2C -------------//
+#ifndef PICO_DEFAULT_I2C
+#define PICO_DEFAULT_I2C 1
+#endif
+
+#ifndef PICO_DEFAULT_I2C_SDA_PIN
+#define PICO_DEFAULT_I2C_SDA_PIN 6
+#endif
+
+#ifndef PICO_DEFAULT_I2C_SCL_PIN
+#define PICO_DEFAULT_I2C_SCL_PIN 7
+#endif
+
+//------------- SPI -------------//
+#ifndef PICO_DEFAULT_SPI
+#define PICO_DEFAULT_SPI 0
+#endif
+
+#ifndef PICO_DEFAULT_SPI_TX_PIN
+#define PICO_DEFAULT_SPI_TX_PIN 3
+#endif
+
+#ifndef PICO_DEFAULT_SPI_RX_PIN
+#define PICO_DEFAULT_SPI_RX_PIN 4
+#endif
+
+#ifndef PICO_DEFAULT_SPI_SCK_PIN
+#define PICO_DEFAULT_SPI_SCK_PIN 2
+#endif
+
+//------------- FLASH -------------//
+
+#define PICO_BOOT_STAGE2_CHOOSE_W25Q080 1
+
+#ifndef PICO_FLASH_SPI_CLKDIV
+#define PICO_FLASH_SPI_CLKDIV 2
+#endif
+
+#ifndef PICO_FLASH_SIZE_BYTES
+#define PICO_FLASH_SIZE_BYTES (2 * 1024 * 1024)
+#endif
+
+// All boards have B1 RP2040
+#ifndef PICO_RP2040_B0_SUPPORTED
+#define PICO_RP2040_B0_SUPPORTED 0
+#endif
+
+#endif