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/Android.mk b/fastboot/Android.mk
index b9b3c92..05ddf2a 100644
--- a/fastboot/Android.mk
+++ b/fastboot/Android.mk
@@ -18,7 +18,7 @@
 
 LOCAL_C_INCLUDES := $(LOCAL_PATH)/../mkbootimg \
   $(LOCAL_PATH)/../../extras/ext4_utils
-LOCAL_SRC_FILES := protocol.c engine.c bootimg.c fastboot.c util.c
+LOCAL_SRC_FILES := protocol.c engine.c bootimg.c fastboot.c util.c fs.c
 LOCAL_MODULE := fastboot
 LOCAL_MODULE_TAGS := debug
 LOCAL_CFLAGS += -std=gnu99