For some reason, a standard reset routine, which is implemented via
CONFIG_SYSRESET_PSCI driver, does not work on C25.

To work around the problem, a new reset driver (CONFIG_SYSRESET_SECO_C25)
is implemented, which performs a system reset by using the onboard STM32
embedded controller (by analogy with the Watchdog functionality).

Herewith CONFIG_SYSRESET_PSCI is disabled in U-Boot config now.

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>