Start writing documentation for kernel development on AM625 which is
present on the BeaglePlay

Signed-off-by: Dhruva Gole <goledhruva@gmail.com>

notecied by shabaz on discord

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

Signed-off-by: Joshua Neal <joshua@trochotron.com>

Using newly added sphinx tabs extension, P8 & P9 cape header pinout diagrams are now easier to navigate.

Added system block diagram and I2C usage block diagram.

Removed double H1 headings

Added BeagleV Ahead to the front page of docs.