samd: Add the Pycubed-Mini V4 board.

ports/samd/boards/PYCUBED_MINI_V04/board.json

@@ -0,0 +1,20 @@
+{
+    "deploy": [
+        "../deploy.md"
+    ],
+    "docs": "https://pocketqube.readthedocs.io/en/latest/",
+    "features": [
+        "Space Ready",
+        "Micro USB",
+        "RGB LED",
+        "SPI Flash"
+    ],
+    "images": [
+        ""
+    ],
+    "mcu": "samd51",
+    "product": "Pycubed Mini V04",
+    "thumbnail": "",
+    "url": "https://pocketqube.readthedocs.io/en/latest/",
+    "vendor": "RexLab"
+}

ports/samd/boards/PYCUBED_MINI_V04/mpconfigboard.h

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+#define MICROPY_HW_BOARD_NAME "PyCubed Mini V4"
+#define MICROPY_HW_MCU_NAME "samd51J19A"
+#define MICROPY_HW_XOSC32K          (1)

ports/samd/boards/PYCUBED_MINI_V04/mpconfigboard.mk

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+MCU_SERIES = SAMD51
+CMSIS_MCU = SAMD51J19A
+LD_FILES = boards/samd51x19a.ld sections.ld
+TEXT0 = 0x4000
+
+# The ?='s allow overriding in mpconfigboard.mk.
+# MicroPython settings
+MICROPY_VFS_LFS1 ?= 1

ports/samd/boards/PYCUBED_MINI_V04/pins.csv

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+# Pin rows contain Pin number and pin name.
+# Pin rows start with PIN_
+# LED rows start with LED_
+# If the pin name is omitted, the pin number is added as name.
+# Rows for empty entries have to start with '-'
+# Empty lines and lines starting with # are ignored
+
+PIN_PB11,FLASH_CS
+PIN_PB10,FLASH_SCK
+PIN_PA08,FLASH_MOSI
+PIN_PA09,FLASH_MISO
+PIN_PA10,FLASH_WP
+PIN_PA11,FLASH_HOLD
+
+PIN_PA13,SCK
+PIN_PA12,MOSI
+PIN_PA14,MISO
+
+PIN_PB12,SDA1 
+PIN_PB13,SCL1
+PIN_PA17,SDA2
+PIN_PA16,SCL2 
+PIN_PB31,SDA3 
+PIN_PB30,SCL3
+
+PIN_PA05,RF_IO0
+PIN_PA04,RF_IO1
+PIN_PA20,RF_RST
+PIN_PA22,RF_CS
+
+PIN_PB15,CS_CAM
+PIN_PB16,EN_CAM
+PIN_PB00,M_EN
+PIN_PB14,M_FAULT
+PIN_PA19,BURN1
+PIN_PA18,BURN2
+PIN_PB08,CS_SD
+
+PIN_PA23,WDT_WDI
+
+PIN_PA21,NEOPIXEL
+PIN_PA06,BATTERY
+
+PIN_PA24,USB_DM
+PIN_PA25,USB_DP
+PIN_PA26,USB_SOF