arm64: perf: fix group validation when using enable_on_exec

This is a port of cb2d8b34 ("ARM: 7698/1: perf: fix group validation
when using enable_on_exec") to arm64, which fixes the event validation
checking so that events in the OFF state are still considered when
enable_on_exec is true.

Cc: <stable@vger.kernel.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>