powerpc: Convert tests to the new support test-driver

Change the powerpc tests to use <support/test-driver.c>.
Also replace some of pthread calls to its xpthread equivalent.

Tested on ppc64le.

	* sysdeps/powerpc/test-get_hwcap.c: Use <support/test-driver.c>
	instead of test-skeleton.c.
	(do_test): Replaced pthread_create and pthread_join with
	xpthread_create and xpthread_join.  Use TEST_VERIFY_EXIT macro.
	Removed unneeded status variable.
	* sysdeps/powerpc/test-gettimebase.c: Use <support/test-driver.c>
	instead of test-skeleton.c.
	* sysdeps/powerpc/tst-tlsopt-powerpc.c: Likewise.