boards: frdm_mcxa166, frdm_mcxa276: add ostimer support

1. add the ostimer
2. by default, the systick is used.
3. The ostimer could be tested with below configure in xxx.overlay:
&systick {
    status = "disabled";
};

&ostimer0 {
    status = "okay";
};
And below configure in xxx.conf:
CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=1000000

Signed-off-by: Peter Wang <chaoyi.wang@nxp.com>