tools: Set the tool's default binary name

This patch: fafd3ec9c assumes that tools must build from
the main makefile folder.
This assumption leads to the error when somebody wants to
build a tool from the tool's folder.
Hence changes are done to provide the default binary name
in the tool's makefile.

Change-Id: Iae570a7f8d322151376b6feb19e739300eecc3fc
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/tools/encrypt_fw/Makefile b/tools/encrypt_fw/Makefile
index ebbc66a..6eb6fae 100644
--- a/tools/encrypt_fw/Makefile
+++ b/tools/encrypt_fw/Makefile
@@ -7,6 +7,7 @@
 V		?= 0
 BUILD_INFO	?= 1
 DEBUG		:= 0
+ENCTOOL		?= encrypt_fw${BIN_EXT}
 BINARY		:= $(notdir ${ENCTOOL})
 OPENSSL_DIR	:= /usr