board: ti: am62x: am62x: Change splashimage and splashsource

Change splashimage which is bmp image loadaddr to 0x80200000 since stack
is situated at 0x80477660 as splash framework requires bmp image to be
present above stack.

Change splashsource to sf to support loading bmp image from ospi flash
memory.

Signed-off-by: Nikhil M Jain <n-jain1@ti.com>