perf/dwc_pcie: Always register for PCIe bus notifier

perf/dwc_pcie: Always register for PCIe bus notifier

When the PCIe devices are discovered late, the driver can't find
the PCIe devices and returns in the init without registering with
the bus notifier. Due to that the devices which are discovered late
the driver can't register for this.

Register for bus notifier & driver even if the device is not found
as part of init.

Fixes: af9597adc2f1 ("drivers/perf: add DesignWare PCIe PMU driver")
Signed-off-by: Krishna chaitanya chundru <quic_krichai@quicinc.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Link: https://lore.kernel.org/r/20240816-dwc_pmu_fix-v2-3-198b8ab1077c@quicinc.com
Signed-off-by: Will Deacon <will@kernel.org>