dt-binding: serial: tegra: add new chips

Add new compatible string for Tegra186. It differs from earlier chips
as it has FIFO mode enable check and 8 byte DMA buffer.
Add new compatible string for Tegra194. Tegra194 has different error
tolerance levels for baud rate compared to older chips.

Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Link: https://lore.kernel.org/r/1567572187-29820-6-git-send-email-kyarlagadda@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>