watchdog: qcom: Add max timeout check to prevent overflow

watchdog: qcom: Add max timeout check to prevent overflow

Added a check to ensure the requested timeout does not exceed the
hardware's maximum supported value. This prevents register overflow
and ensures watchdog reliability.

So, added a check in qcom_wdt_start() to ensure the requested timeout
does not exceed the hardware-supported maximum value. If the requested
value exceeds the maximum value, then the timeout is clamped
at maximum value.

The timeout is first converted to watchdog ticks and then compared
against QCOM_WDT_MAX_TIMEOUT. This helps prevent misconfiguration
and potential watchdog misbehavior due to overflow.

QCOM_WDT_MAX_TIMEOUT is set to 0xFFFFF, as Qualcomm SoCs typically
use 20 bits to store bark/bite timeout values.

This work builds upon the previous submission:
https://lore.kernel.org/u-boot/20250527124926.128413-1-balaji.selvanathan@oss.qualcomm.com/

Signed-off-by: Gopinath Sekar <gopinath.sekar@oss.qualcomm.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Link: https://patch.msgid.link/20250625094607.1348494-1-gopinath.sekar@oss.qualcomm.com
Signed-off-by: Casey Connolly <casey.connolly@linaro.org>