lib/log: Proper reentrant logging

[notYuriy]

Reentrant logging, as it is implemented now, is barely useful. The only way reentracy could be helpful is iff there is an exception in the log function itself. However, this probably means that log state is corrupted anyways and log should not be trusted. Instead, there should be a trusted subset of log_nolock that would handle exceptions in log itself. For example, it can just output to e9.

[N00byEdge]

However, this probably means that log state is corrupted anyways and log should not be trusted.

Remember that each log subsystem (vesa_log, vga_log, platform) etc won't be reentered if you're inside them. If one of them panics, the other ones will print its panic message.