ARM: tegra: Initialize flow controller from DT

Use a matching device tree node to initialize the flow controller driver
instead of hard-coding the I/O address. This is necessary to get rid of
the iomap.h include, which in turn make it easier to share this code
with 64-bit Tegra SoCs.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>