pci_host_generic: remove unneeded ThunderX2 quirk

The current quirk implementation writes a fixed address to the PCI BAR
to fix a firmware bug. The PCI BARs are allocated by firmware and will
change depending on PCI devices present. So using a fixed address here
is not correct.

This quirk worked around a firmware bug that programmed the MSI-X bar
of the SATA controller incorrectly. The newer firmware does not have
this issue, so it is better to drop this quirk altogether.

Reviewed by: andrew
Differential Revision: https://reviews.freebsd.org/D17655