Add Elf64 docs.
Add function_scope logger.
Use function_scope logger.
Use shared debug output macros.
Display name of undefined symbol.
Fix gdt limit calculation edge case.
Move CR0 and CR4 handling to x86_cpu_t from ia32_mmu_t. Fix cr4 bug.

The old code was causing cr4 to not update, because of assembler
assigning both %0 and %1 to eax.
Force inlining of simple inline assembly functions.
Add more CR4 fields.
Update documentation.
Remove unused variable from linker script.
Rename wrmsr to write_msr. Add read_msr. Force assembly functions inline.
Add pcibus module to image by default.
Add some debugging output.
Use function from logger instead of custom one.
Switch headers due to cr0/cr4 handling code moved.