dt-bindings: mtd: ti,gpmc-onenand: Convert to yaml

Convert gpmc-onenand.txt to ti,gpmc-onenand.yaml.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>