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

commit b74b8aa55a43cd00e63af1bf8bbc24a4d6240706 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/+/106716
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>