x86/APIC: make connections between seemingly arbitrary numbers

x86/APIC: make connections between seemingly arbitrary numbers

Making adjustments to arbitrarily chosen values shouldn't require
auditing the code for possible derived numbers - such a change should
be doable in a single place, having an effect on all code depending on
that choice.

For one make the TDCR write actually use APIC_DIVISOR. With the
necessary mask constant introduced, also use that in vLAPIC code. While
introducing the constant, drop APIC_TDR_DIV_TMBASE: The bit has been
undefined in halfway recent SDM and PM versions.

And then introduce a constant tying together the scale used when
converting nanoseconds to bus clocks.

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>