drivers: mrvl_swup: Add debug flag for SMC calls

commit 33fe9a4b29fa646ad44e018a75a030d60a4cea4e from
git@git.assembla.com:cavium/WindRiver.linux.git

Introduce debug flag to enable additional timing stats logging.

Change-Id: I2bb255e6512ee45d9770ce5924ea5660df6e9275
Signed-off-by: Sebastien Dubois <sebastien.dubois@nokia.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/106715
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Tested-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>