ARM: mvebu: a38x: move definition of PEX_CFG_DIRECT_ACCESS

PEX_CFG_DIRECT_ACCESS was defined in ddr3_hws_hw_training_def.h despite
only being used in the serdes code. Move this definition to ctrl_pex.h
where all the other PEX defines are. Also remove the duplicate
definition of PEX_DEVICE_AND_VENDOR_ID which is already defined in
ctrl_pex.h.

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