arm64: perf: Extend event config for ARMv8.1

Perf has supported ARMv8.1 feature with 16-bit evtCount filed [see c210ae80


arm64: perf: Extend event mask for ARMv8.1], event config should be
extended to 16-bit too, otherwise, if use -e event_name whose event_code
is more than 0x3ff, pmu_config_term will return -EINVAL because function
pmu_format_max_value depends on event config.

This patch extends event config to 16-bit.

Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>