PCI: ixp4xx: Guard ARM32-specific hook_fault_code()

PCI: ixp4xx: Guard ARM32-specific hook_fault_code()

hook_fault_code() is an ARM32-specific API.  Guard it and related code with
CONFIG_ARM #ifdefs and remove the ARM arch dependency from Kconfig so the
driver can be compile tested on other architectures.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
[mani: dropped the ARM arch Kconfig dependency]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Acked-by: Linus Walleij <linus.walleij@linar.org>
Link: https://patch.msgid.link/20250925202738.2202195-1-helgaas@kernel.org