Optimizations to the AT keyboard driver to reduce unnecessary delays during the FreeBSD boot process

[bllgg]

Summary of changes

• Introduced a new loader tunable hw.atkbd.fast_delay to /boot/loader.conf.
  • When enabled, the driver uses atkbd_short_delay, which applies significantly shorter delays in the following routines:
    • empty_both_buffers()
    • reset_aux_dev()
    • test_controller()
    • reset_kbd()
  • New short delays are up to 1000× smaller (for buffer resets) and about 40× smaller (for controller and keyboard resets).
  • Default behaviour remains with shorter delays, and hw.atkbd.short_delay should be set to 0, if someone needs longer delays for the old, slower hardware
• Added a separate conf file into the /sys/amd64/conf named BOOT_PROF to enable the TSlogs

Notes:

This patch is part of the ongoing GSoC 2025 work on FreeBSD boot process optimisation.

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