add nugget and nibble boards for 38c3 (#5609)

* add nugget and nibble boards for 38c3

* mark those boards extra for now

variants/nibble_rp2040/platformio.ini

@@ -0,0 +1,17 @@
+[env:nibble-rp2040]
+extends = rp2040_base
+board = rpipico
+board_level = extra
+upload_protocol = picotool
+
+# add our variants files to the include and src paths
+build_flags = ${rp2040_base.build_flags} 
+  -DPRIVATE_HW
+  -Ivariants/nibble_rp2040
+  -DDEBUG_RP2040_PORT=Serial
+  -DHW_SPI1_DEVICE
+  -L "${platformio.libdeps_dir}/${this.__env__}/bsec2/src/cortex-m0plus"
+lib_deps =
+  ${rp2040_base.lib_deps}
+debug_build_flags = ${rp2040_base.build_flags}, -g
+debug_tool = cmsis-dap ; for e.g. Picotool

variants/nibble_rp2040/variant.h

@@ -0,0 +1,18 @@
+#define ARDUINO_ARCH_AVR
+
+#define BUTTON_PIN -1 // Pin 17 used for antenna switching via DIO4
+
+#define LED_PIN 1
+
+#define HAS_CPU_SHUTDOWN 1
+
+#define USE_RFM95
+#define LORA_SCK 10
+#define LORA_MISO 12
+#define LORA_MOSI 11
+#define LORA_CS 13
+
+#define LORA_DIO0 14
+#define LORA_RESET 15
+#define LORA_DIO1 RADIOLIB_NC
+#define LORA_DIO2 RADIOLIB_NC