ACPI timer will be used for the system clock now (in HEAD)

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

    I've just committed work that adds support for the ACPI timer in 
    DragonFly.  Hopefully I haven't blown anything up too badly.

    There are some hacks in place.  Right now the 8254 interrupt timer
    reload code does a 64 bit multiplication and division... obviously
    not what we want to do!  I will calculate a smaller multiplication and
    division value to convert the system clock frequency into the 8254
    frequency.  Since the ACPI clock is an integer multiple of the 8254 
    clock we can easily optimize that, and I will do so in a followup
    commit.

    It is not currently possible to change the clock source after boot.
    I am considering whether to implement it but it would require going to
    a normalized 64 bit sysclock value and I'm leaning against that...
    so the time source chosen at boot will be the one the system has to
    live with.

						-Matt