Enable display for J784S4 EVM.

Add assigned clocks for DSS, DT node for DisplayPort PHY and pinmux for
DP HPD. Add the clock frequency for serdes_refclk.

Add the endpoint nodes to describe connection from:
DSS => MHDP => DisplayPort connector.

Also add the GPIO expander-4 node and pinmux for main_i2c4 which is
required for controlling DP power. Set status for all required nodes
for DP-0 as "okay".
Signed-off-by: Rahul T R <r-ravikumar@ti.com>
[j-choudhary@ti.com: move all the changes together to enable DP-0 in EVM]
Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
Reviewed-by: Aradhya Bhatia <a-bhatia1@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20231019054022.175163-5-j-choudhary@ti.comSigned-off-by: Vignesh Raghavendra <vigneshr@ti.com>