dt-bindings: arm: fsl: Add the librem 5 Evergreen revision

dt-bindings: arm: fsl: Add the librem 5 Evergreen revision

Add an entry for the Librem 5 phone, Evergreen revision which is supported
by "r4". Schematics and more information can be found at
https://developer.puri.sm/Librem5/Hardware_Reference/Evergreen.html

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>