MAINTAINERS: add maintainers for DesignWare PCIe PMU driver

Add maintainers for Synopsys DesignWare PCIe PMU driver and driver
document.

Signed-off-by: Shuai Xue <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Will Deacon <[e-mail]>

MAINTAINERS

···
 S:	Maintained
 F:	drivers/mmc/host/dw_mmc*
 
+SYNOPSYS DESIGNWARE PCIE PMU DRIVER
+M:	Shuai Xue <[e-mail]>
+M:	Jing Zhang <[e-mail]>
+S:	Supported
+F:	Documentation/admin-guide/perf/dwc_pcie_pmu.rst
+F:	drivers/perf/dwc_pcie_pmu.c
+
 SYNOPSYS HSDK RESET CONTROLLER DRIVER
 M:	Eugeniy Paltsev <[e-mail]>
 S:	Supported