rockchip: ringneck-px30: always reset STM32 companion controller on boot

It's happened that glitches on the STM32_RST and STM32_BOOT lines have
put the STM32 companion microcontroller into DFU mode making it not boot
its FW, rendering it useless for the user.

Considering that the STM32 companion microcontroller is always reset on
a reboot or power cycle, resetting it once again in U-Boot SPL isn't
going to hurt it any more.

For ATtiny companion microcontroller, the situation is a bit different
because a reboot or power cycle doesn't reset it. Additionally, since it
can only be reset with a UPDI reset on the STM32_RST line, and that is
virtually impossible to mistakenly trigger, the ATtiny is unlikely to be
in unwanted reset or enter reset because U-Boot toggles STM32_RST line.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>