kernel - Refactor sysclock_t from 32 to 64 bits (2)

* Cputimer reload values can be negative, check condition and
set a small positive reload value instead.

* Also avoids muldivu64() overflow war

kernel - Refactor sysclock_t from 32 to 64 bits (2)

* Cputimer reload values can be negative, check condition and
set a small positive reload value instead.

* Also avoids muldivu64() overflow warnings on the console.

Reported-by: kworr

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kernel - Refactor sysclock_t from 32 to 64 bits

* Refactor the core cpu timer API, changing sysclock_t from 32
to 64 bits. Provide a full 64-bit count from all sources.

* Implement muldivu64() u

kernel - Refactor sysclock_t from 32 to 64 bits

* Refactor the core cpu timer API, changing sysclock_t from 32
to 64 bits. Provide a full 64-bit count from all sources.

* Implement muldivu64() using gcc's 128-bit integer type. This
functions takes three 64-bit valus, performs (a * b) / d
using a 128-bit intermediate calculation, and returns a 64-bit
result.

Change all timer scaling functions to use this function which
effectively gives systimers the capability of handling any
timeout that fits 64 bits for the timer's resolution.

* Remove TSC frequency scaling, it is no longer needed. The
TSC timer is now used at its full resolution.

* Use atomic_fcmpset_long() instead of a clock spinlock when
updating the msb bits for hardware timer sources less than
64 bits wide.

* Properly recalculate existing systimers when the clock source
is changed. Existing systimers were not being recalculated,
leading to the system failing to boot when time sources had
radically different clock frequencies.

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