log: Change log_cpu_state[_mask]() argument to CPUState

Make them available outside NEED_CPU_H and add documentation.

Signed-off-by: Andreas Färber <afaerber@suse.de>
cpu: Move reset logging to CPUState

This adds reset logging for alpha, unicore32 and xtensa.

Signed-off-by: Andreas Färber <afaerber@suse.de>