x86: fix MTRR initialization if EARLY_AP_STARTUP is used

[royger]

Summary

MTRR handlers are set in {amd64/i686}_mem_drvinit, which is called at
SI_SUB_DRIVERS, and that's too late when EARLY_AP_STARTUP is set because APs
have already started at this point. {amd64/i686}_mrinit is also called too late
for the BSP, since that happens when the memory device is attached, also after
APs have already started.

Move the position to SI_SUB_CPU, and also initialize the state for the BSP, so
that the APs can correctly get to the same state as the BSP.

Sponsored by: Citrix Systems R&D

Test Plan

Not tested on i386, only amd64.

[jhb]

This seems sensible. I suspect it was at SI_SUB_DRIVERS due to being tied to the cdev.

It might be slightly cleaner to turn the init method stored in the 'ops' into a stub instead of adding the 'already initialized' check.

[kib]

The code should be merged into x86/x86_mem.c