Add support for Arduino UNO R4 Wifi

[tyeth]

A user is trying to compile WipperSnapper firmware for the Arduino Uno R4 WiFi, which fails due to two dependecies, one of which is SleepyDog library as it is an unsupported architecture.

adafruit/Adafruit_Wippersnapper_Arduino#527

[tyeth]

Tagging @Carda1989 who raised the initial error when building WipperSnapper.

Someone (us or a contributor) needs to:

• Find a suitable common ARCH flag for R4 series
• Consider sleepydog for the R4 and create appropriate file / defines.