refactor: replace in-tree Event Log Lib w/ submodule

The Event Log Library has been relocated to a separate repository and is
now integrated as a submodule, eliminating the need for in-tree files
and reducing maintenance efforts for TFTF.

Change-Id: I29694f8b3b08bb1d57dd685f6e42dc9f69d241bb
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
diff --git a/.gitmodules b/.gitmodules
index c753963..fe722ec 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -5,3 +5,6 @@
 	path = contrib/libtl
 	url = https://review.trustedfirmware.org/shared/transfer-list-library
 	shallow = true
+[submodule "libeventlog"]
+	path = contrib/libeventlog
+	url = https://gerrit.oss.arm.com/trusted-firmware/libEventLog