drivers/perf: hisi_pcie: Introduce hisi_pcie_pmu_get_event_ctrl_val()

Factor out retrieving of the register value for the
corresponding event from hisi_pcie_config_event_ctrl() into a
new function hisi_pcie_pmu_get_event_ctrl_val() allowing future
reuse.

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240223103359.18669-3-yangyicong@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>