tools: Fix incorrect reference in --help messages

The usage instructions now correctly refer to the script name (__file__) rather
than the module name (__name__) when describing how to call the tools.

Issue-Id: SCM-3529
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: I2d264cb1a15827fd6b1195debe71a283171ab03c