ktap: update to v0.4

Add a check for BR2_PACKAGE_ELFUTILS; if this is enabled, then try to link
against libelf from the elfutils package.  This allows ktap to resolve
symbols in userspace.

The new FFI functionality in ktap is not exposed, as it currently only
supports x86_64...

Signed-off-by: Anders Darander <anders@chargestorm.se>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>