arm: mvebu: AXP: Enhance PCIe port capability configuration

arm: mvebu: AXP: Enhance PCIe port capability configuration

This patch enables the PCIe port specific link capabilities configuration
for Armada XP. The weak function board_sat_r_get() was used to return
a common flag for PCIe Gen1 vs Gen2 capability for all PCIe ports. This
is now changed with this patch to return a bit per PCIe port (4 bits
in this case, bit 0 for PCIe port 0, etc).

The theadorable board uses this new feature to configure PCIe port 0
as Gen1 and all other PCIe ports as Gen2 capable. All other AXP boards
using this function are not changed in the configuration and still
configure all ports as PCIe Gen2.

This patch also removes the parameter "pex_mode" from
board_serdes_cfg_get() as this parameter was not used in any of the
implementations.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Phil Sutter <phil@nwl.cc>