FSP spec: debug registers

[ArthurHeymans]

FSP spec does not document that debug registers cannot be used. Some firmwares use debug register to catch NULL dereferencing which a lot of FSP releases do. This hangs the system as FSP has no exception handler for that.

[6d6178667269747a]

@ArthurHeymans , How do you know that the FSP has a NULL pointer dereference error? Currently I'm facing a problem with my RocketLake FSP too. I enter FSP-M at entry but it didn't return.