[S] Change in coreboot[main]: arch/x86/memcpy.c: Optimize code for 64bit

[Jérémy Compostella (Code Review)]

Attention is currently required from: Arthur Heymans.

Jérémy Compostella has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/78646?usp=email )

Change subject: arch/x86/memcpy.c: Optimize code for 64bit
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Patch Set 2:

(1 comment)

File src/arch/x86/memcpy.c:

https://review.coreboot.org/c/coreboot/+/78646/comment/b0e37991_82a5f6af :
PS2, Line 30: 		: "=&c" (d0), "=&D" (d1), "=&S" (d2)
> I noticed the copy of the remaining byte is missing. […]

BTW, the code in the kernel is:
```
static __always_inline void *__memcpy(void *to, const void *from, size_t n)
{
    int d0, d1, d2;
    asm volatile("rep ; movsl\n\t"
    	     "movl %4,%%ecx\n\t"
    	     "andl $3,%%ecx\n\t"
    	     "jz 1f\n\t"
    	     "rep ; movsb\n\t"
    	     "1:"
    	     : "=&c" (d0), "=&D" (d1), "=&S" (d2)
    	     : "0" (n / 4), "g" (n), "1" ((long)to), "2" ((long)from)
    	     : "memory");
    return to;
}
```
And it does pass the test above.