selftests/powerpc: Run per_event_excludes test on Power8 or later

The per_event_excludes test wants to run on Power8 or later. But
currently it checks that AT_BASE_PLATFORM *equals* power8, which means
it only runs on Power8.

Fix it to check for the ISA 2.07 feature, which will be set on Power8
and later CPUs.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200716122142.3776261-1-mpe@ellerman.id.au

tools/testing/selftests/powerpc/pmu/per_event_excludes.c

@@ -12,6 +12,8 @@
 #include <string.h>
 #include <sys/prctl.h>
 
+#include <asm/cputable.h>
+
 #include "event.h"
 #include "lib.h"
 #include "utils.h"
@@ -23,12 +25,9 @@
 static int per_event_excludes(void)
 {
 	struct event *e, events[4];
-	char *platform;
 	int i;
 
-	platform = (char *)get_auxv_entry(AT_BASE_PLATFORM);
-	FAIL_IF(!platform);
-	SKIP_IF(strcmp(platform, "power8") != 0);
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_ARCH_2_07));
 
 	/*
 	 * We need to create the events disabled, otherwise the running/enabled