plat/marvell: update platform LSP version to 18.12.0

Sync the platform code version with current Marvell LSP.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
diff --git a/plat/marvell/version.mk b/plat/marvell/version.mk
index 16b0a16..e072e12 100644
--- a/plat/marvell/version.mk
+++ b/plat/marvell/version.mk
@@ -1 +1 @@
-SUBVERSION = devel-18.09.1
+SUBVERSION = devel-18.12.0