Recent changes from Bamvor (88baa78d) have standardized the
variable names like TEST_GEN_FILES and removed the need for make targets
all and clean.

These changes bring the intel_pstate test inline with those changes.

Cc: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: NStafford Horne <shorne@gmail.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>