ports: Simplify board feature tags in board.json.

This commit:
- Finds a common set of board feature tags and maps existing features to
  that reduced set.
- Removes some less-useful board feature tags.
- Ensures all MCUs are specified correctly.
- Ensures all boards have a vendor (and fixes some vendor names).

This is to make the downloads page show a less intimidating set of filters.

Work done in conjunction with Matt Trentini <matt.trentini@gmail.com>.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

ports/esp8266/boards/GENERIC/board.json

@@ -4,6 +4,7 @@
     ],
     "docs": "",
     "features": [
+        "External Flash",
         "WiFi"
     ],
     "id": "esp8266",

ports/esp8266/boards/GENERIC_1M/board.json

@@ -4,6 +4,7 @@
     ],
     "docs": "",
     "features": [
+        "External Flash",
         "WiFi"
     ],
     "id": "esp8266-1m",

ports/esp8266/boards/GENERIC_512K/board.json

@@ -4,6 +4,7 @@
     ],
     "docs": "",
     "features": [
+        "External Flash",
         "WiFi"
     ],
     "id": "esp8266-512k",