Implement --no-sysfs

[jrgerber]

       --no-sysfs
          Do not attempt to read DMI data from sysfs files. This is mainly
          useful for debugging.

Read the code to find out what this does exactly: https://github.com/mirror/dmidecode/blob/master/dmidecode.c

[jrgerber]

The feature apparently is used to test on a *nix system that has both sysfs files and another methodology, forcing other methodologies to be tried.

	if (!(opt.flags & FLAG_NO_SYSFS)
	 && (buf = read_file(0, &size, SYS_ENTRY_FILE)) != NULL)

other methodologies:

	/* Next try EFI (ia64, Intel-based Mac, arm64) */
	efi = address_from_efi(&fp);
	switch (efi)
	{
		case EFI_NOT_FOUND:
			goto memory_scan;
		case EFI_NO_SMBIOS:
			ret = 1;
			goto exit_free;
	}

or:

#if defined __i386__ || defined __x86_64__
	if (!(opt.flags & FLAG_QUIET))
		pr_info("Scanning %s for entry point.", opt.devmem);
	/* Fallback to memory scan (x86, x86_64) */
	if ((buf = mem_chunk(0xF0000, 0x10000, opt.devmem)) == NULL)
	{
		ret = 1;
		goto exit_free;
	}