acpi_spmc: Check Intel constraint packages

[obiwac]

Summary

Some firmware inexplicably decides to do non-standard and annoying stuff
here, e.g. the Fujitsu Futro S940 with an Intel Pentium J5005 sometimes
returns the following when calling the DEVICE_CONSTRAINTS function on
the Intel DSM:

Return (Package (0x01)
{
    Zero
})

(Package elements here are supposed to be constraint packages, not just a
single value.)

First reported in the following forum post:

https://forum.netgate.com/topic/201090/2.9.0-beta-leads-to-kernel-panic-on-boot

Reported by: TampertK on forum.netgate.com
Sponsored by: The FreeBSD Foundation

[obiwac]

oops forgot continue

[obiwac]

Move name dup later so no leak if skipped constraint

[olce]

That's certainly good enough. We can add even more checks later.

[olce]

By the way, could you perhaps move all reads to constraint_obj->Package.Elements[] together close to the package size check? That makes it easier to verify that the check is correct.