feat(U-Boot): add remoteproc earlyboot support for AM64x

Documentation for u-boot remoteproc loading and starting on AM64x
devices.

Signed-off-by: Hari Nagalla <hnagalla@ti.com>

Author: h-nagalla

configs/AM64X/AM64X_linux_toc.txt

@@ -33,6 +33,7 @@ linux/Foundational_Components/U-Boot/UG-UART
 linux/Foundational_Components/U-Boot/UG-DDRSS
 linux/Foundational_Components/U-Boot/UG-NAND
 linux/Foundational_Components/U-Boot/UG-Network-K3
+linux/Foundational_Components/U-Boot/UG-RemoteProc
 linux/Foundational_Components/U-Boot/Applications
 linux/Foundational_Components/U-Boot/Apps-SPL-Debug
 linux/Foundational_Components/U-Boot/Apps-SPL-Debug-OpenOCD