mimic: spdk: compile with -march=core2 instead of native

This commit cannot be cherry-picked from master because mimic's SPDK
submodule is based on an older upstream version.

Fixes: http://tracker.ceph.com/issues/25032
Signed-off-by: Nathan Cutler <ncutler@suse.com>

diff --git a/src/spdk b/src/spdk
index dc82989dd2747db0384cafb3b310f2e8792d5c24..f474ce6930f0a44360e1cc4ecd606d2348481c4c 160000 (submodule)
--- a/src/spdk
+++ b/src/spdk
@@ -1 +1 @@
-Subproject commit dc82989dd2747db0384cafb3b310f2e8792d5c24
+Subproject commit f474ce6930f0a44360e1cc4ecd606d2348481c4c