PCI: Add quirk for LS7A to avoid reboot failure

LoongArch inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB

--------------------------------

cc27b735 ("PCI/portdrv: Turn off PCIe services during shutdown")
causes poweroff/reboot failure on systems with LS7A chipset. We found
that if we remove "pci_command &= ~PCI_COMMAND_MASTER" in do_pci_disable
_device(), it can work well. The hardware engineer says that the root
cause is that CPU is still accessing PCIe devices while poweroff/reboot,
and if we disable the Bus Master Bit at this time, the PCIe controller
doesn't forward requests to downstream devices, and also does not send
TIMEOUT to CPU, which causes CPU wait forever (hardware deadlock). This
behavior is a PCIe protocol violation (Bus Master should not be involved
in CPU MMIO transactions), and it will be fixed in new revisions of
hardware (add timeout mechanism for CPU read request, whether or not Bus
Master bit is cleared).

On some x86 platforms, radeon/amdgpu devices can cause similar problems
[1][2]. Once before I wanted to make a single patch to solve "all of
these problems" together, but it seems unreasonable because maybe they
are not exactly the same problem. So, this patch add a new function
pcie_portdrv_shutdown(), a slight modified copy of pcie_portdrv_remove()
dedicated for the shutdown path, and then add a quirk just for LS7A to
avoid clearing Bus Master bit in pcie_portdrv_shutdown(). Leave other
platforms behave as before.

[1] https://bugs.freedesktop.org/show_bug.cgi?id=97980
[2] https://bugs.freedesktop.org/show_bug.cgi?id=98638



Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>