system/core: preparation to pull back interfaces from android/log.h

Point to log/log.h where necessary, define LOG_TAG where necessary.
Accept that private/android_logger.h is suitable replacement for
log/logger.h and android/log.h.

Correct liblog/README

Effectively a cleanup and controlled select revert of
'system/core: drop or replace log/logger.h' and
'system/core: Replace log/log.h with android/log.h'.

Test: compile
Bug: 30465923
Change-Id: Ic2ad157bad6f5efe2c6af293a73bb753300b17a2
diff --git a/libpixelflinger/trap.cpp b/libpixelflinger/trap.cpp
index f00e50a..fa6338a 100644
--- a/libpixelflinger/trap.cpp
+++ b/libpixelflinger/trap.cpp
@@ -15,6 +15,8 @@
 ** limitations under the License.
 */
 
+#define LOG_TAG "pixelflinger-trap"
+
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>