selftests/powerpc: Fix remaining fallout from recent changes

In benchmarks we need to use $(TEST_GEN_PROGS) after we include lib.mk,
because lib.mk does the substitution to add $(OUTPUT).

In math the vmx and fpu names were typoed so they no longer matched
correctly, put back the 'v' and 'f'.

In tm we need to substitute $(OUTPUT) into SIGNAL_CONTEXT_CHK_TESTS so
that the rule matches.

In pmu there is an extraneous ':' on the end of $$BUILD_TARGET for the
clean and install rules, which breaks the logic in the child Makefiles.

Fixes: a8ba798b

 ("selftests: enable O and KBUILD_OUTPUT")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>