fix for no -k flag in objdump

[Ken Yap <Ken.Yap@cmis.CSIRO.AU>]

This information was added to the Etherboot home page
(http://www.slug.org.au/etherboot):

There are reports that new versions of objdump don't support the -k
flag needed to dump binaries. I found that ld can generate the binary
image directly, so objdump is not needed. This will be fixed in the
next Etherboot release. To fix 3.2, do this in the src-32 directory:
Edit Config and append "-oformat binary -s" to LDFLAGS. Edit Makefile
and remove lines with $(OBJDUMP) ... and any preceding $(SIZE) ...
lines. Now look at the suffix of the file required after the ld step,
which will be either .tmp or .bin depending on whether lzhuf is run next
or not and change the .out in the $(LD) line to match.