board: verdin-imx8mp: compact slight different lpddr4 configuration

Deduplicate similar DDRC configurations and LPDDR4 training patterns
by patching a single configuration.

The aim is to reduce the SPL memory footprint and simplify maintenance
of lpddr4_timing.c

Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>