drivers/timer/apic_tsc: use ICR as a fallback timeout event source

This adds support for the local APIC in one-shot mode as the timeout
event source for those cases where the CPU supports invariant TSC but
no TSC deadline capability. It is presented as another timer choice.
Existing Kconfig symbols were preserved to minimize board config
disturbance.

This hybrid approach was implemented kind of backward in the apic_timer
driver but it is far cleaner to carry this here.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>