ARM: mvebu: a38x: sync ddr training code with upstream

This syncs drivers/ddr/marvell/a38x/ with the mv_ddr-armada-17.10 branch
of https://github.com/MarvellEmbeddedProcessors/mv-ddr-marvell.git

.

The upstream code is incorporated omitting the ddr4 and apn806 and
folding the nested a38x directory up one level. After that a
semi-automated step is used to drop unused features with unifdef

  find drivers/ddr/marvell/a38x/ -name '*.[ch]' | \
    xargs unifdef -m -UMV_DDR -UMV_DDR_ATF -UCONFIG_DDR4 \
		-UCONFIG_APN806 -UCONFIG_MC_STATIC \
		-UCONFIG_MC_STATIC_PRINT -UCONFIG_PHY_STATIC \
		-UCONFIG_64BIT

INTER_REGS_BASE is updated to be defined as SOC_REGS_PHY_BASE.

Some now empty files are removed and the ternary license is replaced
with a SPDX GPL-2.0+ identifier.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>