rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option

rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option

Add a Kconfig option to set the default value of the
kernel.panic_on_rcu_stall sysctl, allowing the kernel to be built
with panic-on-RCU-stall enabled by default.

This is useful for high-availability systems that require automatic
recovery (via panic_timeout) when a CPU stall is detected, without
needing userspace to configure the sysctl at boot.

This follows the pattern established by BOOTPARAM_SOFTLOCKUP_PANIC
and BOOTPARAM_HUNG_TASK_PANIC.  The runtime sysctl can still override
the Kconfig default.

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>