kernel: add flexibility to k_cycle_get_32() definition

Some arches may want to define this as an inline function, or
define in core arch code instead of timer driver code.
Unfortunately, this means we need to remove from the footprint
tests, but this is not typically a large function.

Issue: ZEP-1546
Change-Id: Ic0d7a33507da855995838f4703d872cd613a2ca2
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>