ram: k3-ddrss: add am62a controller support

TI's am62a family of SoCs uses a new 32bit DDR controller that shares
much of the same functionality with the existing am64 and j721e
controllers.

Select this controller by default when u-boot is build for the am62a

Signed-off-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>