i2c: mpc: Use i2c-scl-clk-low-timeout-us i2c property

"fsl,timeout" is marked as deprecated and replaced by the
"i2c-scl-clk-low-timeout-us" i2c property.

Use this latter and, in case it is missing, for back
compatibility, check whether we still have "fsl,timeout" defined.

Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Wolfram Sang <wsa@kernel.org>