rp2/boards: Add Seeed XIAO RP2040.

ports/rp2/boards/SEEED_XIAO_RP2040/mpconfigboard.cmake

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+# cmake file for Seeed XIAO RP2040

ports/rp2/boards/SEEED_XIAO_RP2040/mpconfigboard.h

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+// https://www.seeedstudio.com/XIAO-RP2040-v1-0-p-5026.html
+
+#define MICROPY_HW_BOARD_NAME          "Seeed XIAO RP2040"
+#define MICROPY_HW_FLASH_STORAGE_BYTES (1 * 1024 * 1024)
+
+#define MICROPY_HW_SPI0_SCK  (2)
+#define MICROPY_HW_SPI0_MOSI (3)
+#define MICROPY_HW_SPI0_MISO (4)
+
+#define MICROPY_HW_SPI1_SCK  (26)
+#define MICROPY_HW_SPI1_MOSI (27)
+#define MICROPY_HW_SPI1_MISO (28)
+
+// NeoPixel data GPIO12, power GPIO11
+
+// Yellow user LED GPIO18
+// Blue TX LED GPIO16
+// Blue RX LED GPIO17