clocksource/drivers/timer-tegra186: Register all accessible watchdog timers

clocksource/drivers/timer-tegra186: Register all accessible watchdog timers

Tegra186+ SoCs expose multiple watchdog timers, but the driver only
registers WDT(0).

Iterate over num_wdts and, for each WDT, check the SCR (firewall) registers
in the TKE block to determine whether Linux has read and write access.
Register the watchdogs that are accessible.

Signed-off-by: Kartik Rajput <kkartik@nvidia.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://patch.msgid.link/20260507154557.2082697-4-kkartik@nvidia.com