Convert CONFIG_SYS_FSL_PCIE_COMPAT to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FSL_PCIE_COMPAT

To do this, introduce a choice and option for each of the strings used
and set CONFIG_SYS_FSL_PCIE_COMPAT based on that.

Signed-off-by: Tom Rini <trini@konsulko.com>