libcutils: create private/fs_config.h

(cherry picked from commit a9403f0db88d9cdc7ec8627210ae66d3ec250d06)

private/fs_config.h is required in order to build an independent
test that requires internal binary knowledge of the
etc/fs_config_(files|dirs) files.

Test: compile
Bug: 36071012
Change-Id: I268bcfdbb6d45b7bf6040cbf307a4e34812f5fef
diff --git a/libcutils/fs_config.c b/libcutils/fs_config.c
index fdcf22f..a2f5816 100644
--- a/libcutils/fs_config.c
+++ b/libcutils/fs_config.c
@@ -35,22 +35,13 @@
 
 #include <log/log.h>
 #include <private/android_filesystem_config.h>
+#include <private/fs_config.h>
 #include <utils/Compat.h>
 
 #ifndef O_BINARY
 #define O_BINARY 0
 #endif
 
-/* The following structure is stored little endian */
-struct fs_path_config_from_file {
-    uint16_t len;
-    uint16_t mode;
-    uint16_t uid;
-    uint16_t gid;
-    uint64_t capabilities;
-    char prefix[];
-} __attribute__((__aligned__(sizeof(uint64_t))));
-
 /* My kingdom for <endian.h> */
 static inline uint16_t get2LE(const uint8_t* src) { return src[0] | (src[1] << 8); }