arm64: dts: armada-3720-turris-mox: remove mrvl,i2c-fast-mode

Some SFP modules are not detected when i2c-fast-mode is enabled even when
clock-frequency is already set to 100000. The I2C bus violates the timing
specifications when run in fast mode. So disable fast mode on Turris Mox.

Same change was already applied for uDPU (also Armada 3720 board with SFP)
in commit fe3ec631 ("arm64: dts: uDPU: remove i2c-fast-mode").

Fixes: 7109d817

 ("arm64: dts: marvell: add DTS for Turris Mox")
Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <kabel@kernel.org>
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>