tools: Set the tool's default binary name

This patch: fafd3ec9 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>