Log: Share tfm_log.h for different apps

This patch moves tfm_log.h to log so that it can be share by different
apps such as test app and eRPC app.

Change-Id: I0a5e7c72b226e36ef44b852a424375bf0abb670e
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/app/tfm_log.h b/log/tfm_log.h
similarity index 100%
rename from app/tfm_log.h
rename to log/tfm_log.h