PocketBeagle2: Add rust seven segment example

• Using the kernel driver.
• Requires latest devicetree and overlays from here: BeagleBoard-DeviceTrees!109 (merged)
• Also needs the kernel driver which we did not ship in default config before.
• Requires superuser. Would be nice to setup some rules to allow normal users to use them.

Signed-off-by: Ayush Singh ayush@beagleboard.org