target/stm32f7x: clarify reset_config comment

target/stm32f7x: clarify reset_config comment

The reset_config line in the config file does not actually set
connect_assert_srst (the default is connect_deassert_srst), but it reads
as if it does. Clarify that the target is compatible with
connect_assert_srst, without suggesting that the file actually sets it
to that value.

Change-Id: I14e9445ab282d386b5d0055f6adf03d7c8878a8c
Signed-off-by: Christopher Head <chead@zaber.com>
Reviewed-on: http://openocd.zylin.com/4743
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>