ITE drivers/timer: fix tests/drivers/flash build error
ITE drivers/timer: fix tests/drivers/flash build error

There wasn't the build error in PR#44060,
but now tool chain isn't happy about putting the arch_busy_wait()
to __ram_code section, then it shows a build error:
https://github.com/zephyrproject-rtos/zephyr/runs/5755633537?check_suite_focus=true#step:10:933

So I remove __ram_code of arch_busy_wait(), and this will need
extra fetch code time when arch_busy_wait() code isn't in
the dynamic cache.

Verified by follow test pattern:
west build -p auto -b it8xxx2_evb tests/drivers/flash

Signed-off-by: Ruibin Chang <6748d95250dd3d29f04d200035d5434f3b7820ef@ite.com.tw>

zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr