[PATCH v2] Support Intel SHA512

[Jiang, Haochen]

> > --- /dev/null
> > +++ b/gas/testsuite/gas/i386/sha512.d
> > @@ -0,0 +1,16 @@
> > +#as:
> 
> What purpose does this line (present in several of the tests) have?
> 
> > --- /dev/null
> > +++ b/gas/testsuite/gas/i386/sha512.s
> > @@ -0,0 +1,13 @@
> > +# Check 32bit SHA512 instructions
> > +
> > +	.allow_index_reg
> 
> This doesn't look to be needed either.
> 

We use script to generate the testcases so these two are to fit all
circumstances since actually script does not know what will happen
for a new ISA. (The former is for some extra option in as the latter is
for index reg.)

We could omit that but one thing I need to mention is that there are
also some redundant things in all the existing testcases. If we want to
eliminate all of them, some may need careful manual work. I am
wondering if that is time-worthy to change all of them. Therefore, I
propose not to omit that to keep align with all the testcases since it
is not wrong. 

All the other mentioned in the review has been fixed in my v3 patch
which will be sent out later.

Thx,
Haochen