Make Marvell mv_pci.c driver generic

PCI ports differ between Marvell SoCs, but have the same compatible in FDT.
Identification is made based on parent compatible during attach.
For ArmadaXP skipping enable procedure is necessary. To achieve it
sc_skip_enable_procedure flag is used.
For Armada38x find root procedure is necessary. For other SoCs root link is
always at slot 0. sc_enable_find_root_slot flag is used to select proper
behaviour.
Marvell armv5 platforms does not support msi.

Submitted by: Rafal Kozik <rk@semihalf.com>
Reviewed by: andrew
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14735