i2c: mlxbf: remove device tree support

BlueField customers have to use the BlueField firmware with
UEFI ACPI tables so there is no need to have device tree
support in the i2c-mlxbf.c driver. Remove the device tree
binding documentation as well.

Signed-off-by: Asmaa Mnebhi <asmaa@nvidia.com>
Reviewed-by: Khalil Blaiech <kblaiech@nvidia.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>