arm64: dts: marvell: espressobin: Update link to V7 schematic

Up-to-date version of V7 schematic is on new URL linked from official
tech-spec webpage http://espressobin.net/tech-spec/



Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>