tcl/target/stm32(f7/h7)x: do not assume presence of the reset

tcl/target/stm32(f7/h7)x: do not assume presence of the reset

do not force the presence of the reset line, since some custom boards
may do not contain the reset line.

Change-Id: I031ab34012b34a1b49def9db16461f9de0ae29cc
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reported-by: Fleck <fleckz@users.sourceforge.net>
Fixes: https://sourceforge.net/p/openocd/tickets/316/
Reviewed-on: https://review.openocd.org/c/openocd/+/6506
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins