Internal module names for x86 architecture intrinsics

[gnzlbg]

In #166 I've added some architecture intrinsics (e.g. the cpuid intrinsic) to a misc module in x86.

Our internal module names are private and do not affect users, but IMO the name misc is pretty bad and we should group these intrinsics in a more consistent way.

We could name those modules .../i386/i486/i586/i686/... instead.

The main issue I have with this is that, for example, detecting i686 using target feature leads to:

if cfg!(all(target_arch = "x86", not(target_feature = "sse2"))) {

}

is IMO a bit messy.

[gnzlbg]

This split already happened.