treewide: drop executable file attrib for non-executable files
-rw-r--r-- 10361 Makefile
-rw-r--r-- 28560 README.md
-rw-r--r-- 29371 READMEPL.md
drwxr-xr-x - bin
drwxr-xr-x - host_util
drwxr-xr-x - original_u-boot_images
drwxr-xr-x - u-boot