Add documentation for compatible string thead,th1520-i2c which can be used specifically for the TH1520 SoC. Signed-off-by: Thomas Bonnefille <thomas.bonnefille@bootlin.com> Acked-by: Conor Dooley <conor.dooley@microchip.com> Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com> Signed-off-by: Andi Shyti <andi.shyti@kernel.org>