Even when the underlying HW doesn't offer the CHAIN event
(which happens with QEMU), we can always support it as we're
in control of the counter overflow.

Always advertise the event via PMCEID0_EL0.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221113163832.3154370-4-maz@kernel.org