powerpc/fsl_pci: add versionless pci compatible

There are much pci compatible with version on existing platforms.
To stop putting version numbers in device tree later, we add a
generic compatible 'fsl,qoriq-pcie'.
The version number is readable directly from a register.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>