perf/x86/rapl: Fix RAPL config variable bug

This patch fixes a bug introduced by:

  fd3ae1e1

 ("perf/x86/rapl: Move RAPL support to common x86 code")

The Kconfig variable name was wrong. It was missing the CONFIG_ prefix.

Signed-off-by: Stephane Eranian <eraniangoogle.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Kim Phillips <kim.phillips@amd.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200528201614.250182-1-eranian@google.com