arm: a37xx: pci: Do not automatically enable bus mastering on PCI Bridge

Now that PCI Bridge is working for the PCIe Root Port, U-Boot's PCI_PNP
code automatically enables memory access and bus mastering when needed.

We do not need to enable it when setting the HW up.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>