ram: k3-am654: add support for LPDDR4 and DDR3L DDRs

Added training support for LPDDR4 and DDR3L DDRs.  Also added/changed
some register configuration to support all 3 DDR types

Signed-off-by: James Doublesin <doublesin@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>