tests: kernel: Fix assumption in test_kernel_cpu_idle

test_kernel_cpu_idle assumes that CPU's next timer wakeup will be
1 millisecond in the future based on kernel timer it sets. Move tick
synchronization delay into test loop so this will always be the case.

Fixes #41347

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>
1 file changed