mx6sabresd: Convert PCI to driver model

Convert imx6sabresd PCI to driver model to fix the following warning:

===================== WARNING ======================
This board does not use CONFIG_DM_PCI Please update
the board to use CONFIG_DM_PCI before the v2019.07 release.
Failure to update by the deadline may result in board removal.
See doc/driver-model/MIGRATION.txt for more info.
====================================================

After the conversion the following commands were used for testing:

=> pci enum
PCI: Failed autoconfig bar 10
PCI: Failed autoconfig bar 10
=> pci 1
Scanning PCI devices on bus 1
BusDevFun  VendorId   DeviceId   Device Class       Sub-Class
Reviewed-by: Fabio Estevam <festevam@gmail.com>