arm: plat-orion: use mv_mbus_dram_info() in PCIe code

The PCIe code was directly accessing the orion_mbus_dram_info
structure to get access to a description of the SDRAM chip selects in
order to configure the PCIe -> SDRAM address decoding
windows.

However, with the introduction of the orion-mbus driver, we are going
to remove this global structure and instead leave only the exported
mv_mbus_dram_info() function to access this description of the SDRAM
chip selects. Therefore, we simply switch to using this API.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>