Prior to this commit mp_hal_ticks_cpu() was not started properly. It only
started when the code was executed with a debugger attached, except for the
Teensy (i.MXRT1062) boards. As an additional fix, the CYYCNT timer is now
started at boot time.
Also rename mp_hal_ticks_cpu_init() to mp_hal_ticks_cpu_enable().
SysTick cannot wake the CPU from WFI/WFE so a hardware timer is needed to
keep track of ticks/delay (similar to the nrf port).
Fixes issue #7234.
Signed-off-by: Damien George <damien@micropython.org>