x86: Support Intel UINTR

[Cui, Lili]

> On 13.10.2020 08:11, Cui, Lili wrote:
> > --- a/gas/testsuite/gas/i386/prefix.s
> > +++ b/gas/testsuite/gas/i386/prefix.s
> > @@ -367,14 +367,6 @@
> >
> >  	nop
> >
> > -# repz; rdrand %eax
> > -	.byte 0xf3
> > -	.byte 0x0f
> > -	.byte 0xc7
> > -	.byte 0xf0
> > -
> > -	nop
> > -
> 
> Instead of outright dropping this, can you see about finding a suitable
> replacement encoding to retain what's being tested here?
> 
> Jan

Hi Jan,

Thanks for your review, I tried but didn't find a replaceable encoding here，
as RDRAND not support F2/F3 prefixes, so H.J added an invalid test case(repz rdrand %eax) here,
"repz rdrand" encoding is same with "senduipi",  so I have to delete this testcase.


Rdrand  NFx REX.W + 0F C7 /6 

NFx ? Indicates the use of F2/F3 prefixes (beyond those already part of the instructions opcode) are not
allowed with the instruction. Such use will either cause an invalid-opcode exception (#UD) or result in the
encoding for a different instruction.

Thanks,
Lili.