tests: drivers: pwm: pwm_loopback: test improvement.

Move TEST_PWM_PERIOD and TEST_PWM_PULSE to kconfig
and update macro name with "CONFIG_" prefix.

The default timing parameters may be too big for timer
peripheral, because they have high frequence, can not
generate such slow PWM wave.

To keep compatibility, the default value in kconfig
are consistent with the code.

Signed-off-by: Felix Wang <fei.wang_3@nxp.com>
2 files changed