arm64: makefile: fix perf_callchain.o kconfig dependency

Commit 4b3dc967 ("arm64: force CONFIG_SMP=y and remove redundant
#ifdefs") incorrectly resolved a conflict on arch/arm64/kernel/Makefile
which resulted in a partial revert of 52da443e

 ("arm64: perf: factor
out callchain code"), leading to perf_callchain.o depending on
CONFIG_HW_PERF_EVENTS instead of CONFIG_PERF_EVENTS.

This patch restores the kconfig dependency for perf_callchain.o.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>