ARM: dts: sti: extract display subsystem out of soc

ARM: dts: sti: extract display subsystem out of soc

The display subsystem represent how IPs are interacting together and
have nothing to do within the SoC node.

Extract it from the SoC node and let IPs nodes in the Soc node.

Several nodes did not use conventional name:
 * sti-display-subsystem -> display-subsystem
 * sti-controller -> display-controller
 * sti-tvout -> encoder
 * sti-hda -> analog
 * sti-hqvdp -> plane

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Acked-by: Patrice Chotard <patrice.chotard@foss.st.com>
Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Link: https://patch.msgid.link/20250717-sti-rework-v1-3-46d516fb1ebb@gmail.com
Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>