[NTOS:KE][HALX86] Implement AP startup code (#5879)

Co-authored-by: Victor Perevertkin <victor.perevertkin@reactos.org>

Introduce the initial changes needed to get other processors up and into ke

[NTOS:KE][HALX86] Implement AP startup code (#5879)

Co-authored-by: Victor Perevertkin <victor.perevertkin@reactos.org>

Introduce the initial changes needed to get other processors up and into kernel mode.
This only supports x86 as of now but is the first real step towards using other system processors.

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