Fix the timeout issue after running "bootp" command in u-boot
console. For example you see "EHCI timed out on TD- token=0x...".
TXFIFOTHRES bits of TXFILLTUNING register should be set to 0x10
after a controller reset and before RUN bit is set
(per technical reference manual).

Signed-off-by: Jim Lin <jilin@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>