drivers/timer/cavs_timer: Don't suppress smp_timer_init()

This function wasn't being defined when SMP_BOOT_DELAY was set or when
SMP wasn't enabled.  There's no reason for either, then function
doesn't depend on any kconfig-dependent build-time state, and (given
that we use -ffunction-sections) it won't appear in output binaries
unless called.

And there are use cases (e.g. z_smp_start_cpu()) where we need that
function even when BOOT_DELAY is enabled.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>