spi: tegra: documentation for optional fields

Binding doc for optional fields added for TEGRA
SPI contorllers.

Bug 1788947
Bug 200195268

Change-Id: I86f426c0002b5ce8c8f9ed44818385e9b2323853
Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Reviewed-on: http://git-master/r/1215496
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>
1 file changed