cortex_a: get rid of not needed log messages

cortex_a: get rid of not needed log messages

when using semi-hosting with cortex_a this LOG_INFO pollutes openocd
console, so just reduce the log level of this message.

Change-Id: I91aa70492f4e361b25a0e5517d0cf73f2f8ed599
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://gerrit.st.com/c/stm32ide/official/openocd/+/248225
Tested-by: Tarek BOCHKATI <tarek.bouchkati@st.com>
Reviewed-by: Tarek BOCHKATI <tarek.bouchkati@st.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6993
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>