[Beignet] [PATCH 4/4] gbe: Implement a new BTI solution to support dynamic bti

[Song, Ruiling]

> One tricky way is to use a different flag and put the store/restore instruction
> out of the while loop. For example, if we get an allocated f0.1 then use f1.1
> as well,
> Please refer the following instructions:
> 
>   mov(1) g121.14<2>:UW f1.1
>   mov    f1.1<2>:UW  0x0UW
>   ...
>   while(16) -xx
>   mov(1) f1.1  g121.14<0,1,0>
> 
> We may save some instructions if it iterates more than once.

> Why not use a UW type for the BTI register? Then we can only generate one
> CMP instruction under SIMD16 mode.
> 
> There are also some other comments embedded in the patch,
Only above two things not done in v2, I would leave it later.
The UW type need some careful consideration, as the next patch to support storing/loading pointer have some dependency on this.
The flag register should be easy job, I will do it very soon.