fsl_pci: Update PCIe boot ouput

This change does the following:
- Adds printing of negotiated link width.  This information can be
  useful when debugging PCIe issues.
- Makes it optional for boards to implement board_serdes_name().
  Previously boards that did not implement it would print unsightly
  output such as "PCIE1: Connected to <NULL>..."
- Rewords the PCIe boot output to reduce line length and to make it
  clear that the "base address XYZ" value refers to the base address of
  the internal processor PCIe registers and not a standard PCI BAR
  value.
- Changes "PCIE" output to the standard "PCIe"

Before change:
PCIE1: connected to <NULL> as Root Complex (base addr ef008000)
  01:00.0     - 10b5:8518 - Bridge device
   02:01.0    - 10b5:8518 - Bridge device
   02:02.0    - 10b5:8518 - Bridge device
   02:03.0    - 10b5:8518 - Bridge device
PCIE1: Bus 00 - 05
PCIE2: connected to <NULL> as Endpoint (base addr ef009000)
PCIE2: Bus 06 - 06

After change:
PCIe1: Root Complex of PEX8518 Switch, x4, regs @ 0xef008000
  01:00.0     - 10b5:8518 - Bridge device
   02:01.0    - 10b5:8518 - Bridge device
   02:02.0    - 10b5:8518 - Bridge device
   02:03.0    - 10b5:8518 - Bridge device
PCIe1: Bus 00 - 05
PCIe2: Endpoint of VPX Fabric A, x2, regs @ 0xef009000
PCIe2: Bus 06 - 06

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>