mkfs: validate logarithmic parameters sanely

mkfs: validate logarithmic parameters sanely

Testing logarithmic paramters like "-n log=<num>" shows that we do a
terrible job of validating such input. e.g.:

.....
naming   =version 2              bsize=65536  ascii-ci=0 ftype=0
....

Yeah, I just asked for a block size of 2^456858480, and it didn't
get rejected. Great, isn't it?

So, factor out the parsing of logarithmic parameters, and pass in
the maximum valid value that they can take. These maximum values
might not be completely accurate (e.g. block/sector sizes will
affect the eventual valid maximum) but we can get rid of all the
overflows and stupidities before we get to fine-grained validity
checking later in mkfs once things like block and sector sizes have
been finalised.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Jan Tulak <jtulak@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>