arm64: Select POSIX_CPU_TIMERS_TASK_WORK

With 6caa5812e2 ("KVM: arm64: Use generic KVM xfer to guest work
function") all arm64 exit paths are properly equipped to handle the
POSIX timers' task work.

Deferring timer callbacks to thread context, not only limits the amount
of time spent in hard interrupt context, but is a safer
implementation[1], and will allow PREEMPT_RT setups to use KVM[2].

So let's enable POSIX_CPU_TIMERS_TASK_WORK on arm64.

[1] https://lore.kernel.org/all/20200716201923.228696399@linutronix.de/
[2] https://lore.kernel.org/linux-rt-users/87v92bdnlx.ffs@tglx/

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211018144713.873464-1-nsaenzju@redhat.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/Kconfig

@@ -192,6 +192,7 @@ config ARM64
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
+	select HAVE_POSIX_CPU_TIMERS_TASK_WORK
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select MMU_GATHER_RCU_TABLE_FREE