When reading from a dump file, read_file would be more convenient to
use than mem_chunk, but it lacks an offset parameter.

Signed-off-by: Jean Delvare <jdelvare@suse.de>

Let read_file return the actual data size to the caller. This gives
the caller the possibility to check that the data size is as expected
and large enough for the purpose, and report to the user if not.

We can easily support 64-bit addresses by compiling dmidecode with
-D_FILE_OFFSET_BITS=64. This looks reasonably portable.

Also add support for 32-bit long tables, as SMBIOS 3.0.0 allows it,
even though I don't expect to see such a long DMI table any time soon.

Add a function that can read a complete, unknown size file for
reading entry point files from sysfs.  This function models its signature
on the mem_chunk() funtion, so it also allocates memory that the caller
needs to free.  The files that we are interested in reading are very small,
and have a known upper bound on the size.  The EINTR handling is based
on the myread() function.

Contributed by Roy Franz.

u64 values.