armv7R: K3: am654: Trigger panic on DDR init failures

armv7R: K3: am654: Trigger panic on DDR init failures

When initializing DDR from R5 SPL trigger U-Boot's panic facility
rather than simply returning from the board init function as there
is little point continuing code execution. Further, as panic implies
a board reset, so using it might potentially allow to recover from
this error in certain cases such as when the init failure was caused
by a temporary glitch of some sorts.

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>