add a variant based on the nrf52840-dk but with a RC clock.

Because I was dumb and accidentally ran some code that configured gpio 0
as an output and that was enough to smoke the xtal that was preinstalled
between P0.0 and P0.1.

boards/ppr.json

@@ -0,0 +1,46 @@
+{
+  "build": {
+    "arduino": {
+      "ldscript": "nrf52840_s140_v6.ld"
+    },
+    "core": "nRF5",
+    "cpu": "cortex-m4",
+    "extra_flags": "-DARDUINO_NRF52840_PPR -DNRF52840_XXAA",
+    "f_cpu": "64000000L",
+    "hwids": [["0x239A", "0x4403"]],
+    "usb_product": "PPR",
+    "mcu": "nrf52840",
+    "variant": "pca10056-rc-clock",
+    "variants_dir": "variants",
+    "bsp": {
+      "name": "adafruit"
+    },
+    "softdevice": {
+      "sd_flags": "-DS140",
+      "sd_name": "s140",
+      "sd_version": "6.1.1",
+      "sd_fwid": "0x00B6"
+    },
+    "bootloader": {
+      "settings_addr": "0xFF000"
+    }
+  },
+  "connectivity": ["bluetooth"],
+  "debug": {
+    "jlink_device": "nRF52840_xxAA",
+    "onboard_tools": ["jlink"],
+    "svd_path": "nrf52840.svd"
+  },
+  "frameworks": ["arduino"],
+  "name": "Meshtastic PPR (Adafruit BSP)",
+  "upload": {
+    "maximum_ram_size": 248832,
+    "maximum_size": 815104,
+    "require_upload_port": true,
+    "speed": 115200,
+    "protocol": "jlink",
+    "protocols": ["jlink", "nrfjprog", "stlink"]
+  },
+  "url": "https://meshtastic.org/",
+  "vendor": "Othernet"
+}