boards: stm32h7: Update openocd runner to specify target handle

Openocd scripts for STM32H7 SoCs use _CHIPNAME.cpu{0|1} as
target handle.
Specify this thanks to new openocd runner option '-target-handle'.

This is required to allow thread awareness debugging on these targets.

Fixes #45778

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>