Change in coreboot[master]: soc/skylake: Make VT-d controllable from CMOS option

[Nico Huber (Code Review)]

Attention is currently required from: Sean Rhodes, Patrick Rudolph.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/56252 )

Change subject: soc/skylake: Make VT-d controllable from CMOS option
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Patch Set 6:

(2 comments)

File src/soc/intel/skylake/systemagent.c:

https://review.coreboot.org/c/coreboot/+/56252/comment/0bb69a29_88f76d6a 
PS6, Line 18: bool soc_is_vtd_capable(void)
Could we rename this to make it clear that it does more now? e.g.
`soc_vtd_enabled()`.

https://review.coreboot.org/c/coreboot/+/56252/comment/9d9de05b_48ac6b14 
PS6, Line 23: (!vtd) & VTD_DISABLE)
Isn't this part constant 0?

How about a simple bail-out on top if the user wants it disabled:

const unsigned int vtd = get_uint_option("vtd", 1);
    if (!vtd)
            return false;