Documentation: synopsys-dw-mshc: add binding for fifo quirks

Add fifo-addr property and fifo-watermark-quirk property to
synopsys-dw-mshc bindings. It is intended to provide more
dt interface to support SoCs specific configuration.

Signed-off-by: Jun Nie <jun.nie@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>