- map the hard-coded frame buffer address above KERNBASE. Using the
physical address only worked because of larger mapping bugs.
The hard-coded frame buffer address only works on x86. Use messy ifdefs
to try to avoid warnings about unused code for other arches.
- remove the sysctl for reading and writing the table kernel console
attributes. Writing only worked for emergency output since normal
output uses unalterd copies.
- fix the test for the emergency console being usable
- explain why a hard-coded attribute is used very early. Emergency output
works on x86 even before the pcpu pointer is initialized.
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