zephyr: volteer: Set fan PWM to output open-drain
zephyr: volteer: Set fan PWM to output open-drain

CROS Volteer fan PWM has PWM_CONFIG_OPEN_DRAIN flag which sets the PWM
to output open drain. Set Zephyr Volteer fan PWM to output open-drain
to meet the original setting.

BUG=none
BRANCH=none
TEST=Check pwm5 set to output open-drain by 'rw'.

Cq-Depend: chromium:2845386
Signed-off-by: Wealian Liao <b980917544b235741b592c0c8e1e53fb264e55ff@nuvoton.corp-partner.google.com>
Change-Id: I43c5b4b95b04f4a38bf123f3691b165f541ad7e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2847863
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Commit-Queue: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec