arch_timer.h includes linux/smp.h since the commit:

  6acc71cc ("arm64: arch_timer: Allows a CPU-specific erratum to only affect a subset of CPUs")

It was included to use DEFINE_PER_CPU(), etc. But It should have
included <linux/percpu.h> rather than <linux/smp.h>. It worked because
smp.h includes percpu.h.

The next commit will remove percpu.h from smp.h and it will break this
usage.

Explicitly include percpu.h and remove smp.h
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20240503171847.68267-1-puranjay@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>