fwts should not access /dev/mem on aarch64 (acpi mcfg failure)

On aarch64 fwts tries to mmap the PCI config space in compare_config_space (src/acpi/mcfg/mcfg.c) which fails when the kernel options CONFIG_STRICT_DEVMEM / CONFIG_IO_STRICT_DEVMEM are set - which nowadays is the default configuration.

From debian/changelog it appears this might have been fixed in the 18.12 release but then broken again in 20.11:

  [Heinrich Schuchardt]
  * README: document required kernel configuration
  * lib: avoid bus error in fwts_safe_memcpy
  * lib: enable /dev/mem access on aarch64
...
  [Leif Lindholm]
  * lib: disable /dev/mem access on aarch64
  * dmicheck: drop unaligned memcpy
  * lib: drop fwts_memcpy_unaligned
  * dmicheck: use dmi_load_file in preference to fwts_mmap