docs: perf: Update usage for target filter of hisi-pcie-pmu

docs: perf: Update usage for target filter of hisi-pcie-pmu

One of the "port" and "bdf" target filter interface must be set, and
the related events should preferably used in the same group.
Update the usage in the documentation.

Signed-off-by: Junhao He <hejunhao3@huawei.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240223103359.18669-9-yangyicong@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>