configs: am4xhs: Modify SPL load address to fix UART boot issue

configs: am4xhs: Modify SPL load address to fix UART boot issue

An issue in the TI secure image generation tool causes the ROM to
load the SPL at a different load address than what is specified by
CONFIG_ISW_ENTRY_ADDR while doing a peripheral boot on HS devices.

This causes the SPL to fail on secure devices during peripheral
boot.

The TI secure image generation tool has been fixed so that the SPL
will always be loaded at 0x403018E0 by the ROM code for both
peripheral and memory boot modes.

Signed-off-by: Madan Srinivas <madans@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>
Acked-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>