x86/intel_rdt: Select KERNFS when enabling INTEL_RDT_A

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c: In function 'rdtgroup_kn_lock_live':
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c:658:2: error: implicit declaration of
function 'kernfs_break_active_protection' [-Werror=implicit-function-declaration]

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Shaohua Li <shli@fb.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>