fastboot: allow format on devices with small buffers

Formatting large partitions on devices with small transfer buffers did
not work before since format used a strange path through the code to
send data. It now uses the normal path. Also cleaned up a bit. FS
code now lives in a separate file and the custom path for format is
gone.

Change-Id: If4e01cabc2e250b7c02ca7ce8c268e51d49e1529
diff --git a/fastboot/fs.h b/fastboot/fs.h
new file mode 100644
index 0000000..65b9555
--- /dev/null
+++ b/fastboot/fs.h
@@ -0,0 +1,12 @@
+#ifndef _FS_H_
+#define _FH_H_
+
+#include <stdint.h>
+
+struct fs_generator;
+
+const struct fs_generator* fs_get_generator(const char* name);
+int fs_generator_generate(const struct fs_generator* gen, int tmpFileNo, long long partSize);
+
+#endif
+