video: tidss: Use DT property names for parsing nodes

Use device-tree node property names for parsing nodes instead of
indexing as indexing could be different between different SoCs based on
number of DSS entities available on that particular SoC.

Also correct the video layer naming in driver to match to actual one
being used in upstream DSS device-tree node [1].

This also fixes AM62x splash screen usage using the latest upstream DSS
device-tree nodes where hard-coded indexing which driver was using
before this patch was not matching the correct properties in the DT
node.

[1]: Upstream AM62x DSS node:
https://github.com/torvalds/linux/blob/v6.8-rc1/arch/arm64/boot/dts/ti/k3-am62-main.dtsi#L774



Fixes: 5f9f816b ("drivers: video: tidss: TIDSS video driver support for AM62x")
Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
Reviewed-by: Nikhil M Jain <n-jain1@ti.com>