libexif: rewrite ptest handling

libexif: rewrite ptest handling

What started as replacing the installation of libtool wrapper scripts
ended up being a rewrite of the ptest integration.

There are only ~15 tests so we can install the binaries with libtool,
extract the test names from the Makefile, and just run them with a few
lines of shell.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>