build: Set mode for makefiles

* These shouldn't be executable.

Change-Id: Idcb4e46f0ac69116b4837cd31f9f2e506b41a3f2
diff --git a/build/core/mtk_utils.mk b/build/core/mtk_utils.mk
old mode 100755
new mode 100644
diff --git a/build/core/qcom_utils.mk b/build/core/qcom_utils.mk
old mode 100755
new mode 100644
diff --git a/build/core/sdllvm-lto-defs.mk b/build/core/sdllvm-lto-defs.mk
old mode 100755
new mode 100644