PCI: mvebu: Setup PCIe controller to Root Complex mode

PCI: mvebu: Setup PCIe controller to Root Complex mode

BugLink: https://bugs.launchpad.net/bugs/1964361
[ Upstream commit df08ac016124bd88b8598ac0599d7b89c0642774 ]

This driver operates only in Root Complex mode, so ensure that hardware is
properly configured in Root Complex mode.

Link: https://lore.kernel.org/r/20211125124605.25915-10-pali@kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>