drivers: mrvl_swup: clear SMC log buffer for each SMC call

commit 1e1c40f48649ad04210959acb4c417a8d7ae056e from
git@git.assembla.com:cavium/WindRiver.linux.git

Each time a log buffer is needed for SMC call, clear its content
even it was already allocation before.
Add info trace for each SMC call.

Change-Id: Ie451039df4b95d2fd9bbed638f993046fe119088
Signed-off-by: Sebastien Dubois <sebastien.dubois@nokia.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/106699


Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Li Wang <li.wang@windriver.com>