MAINTAINERS: Add entry for Qualcomm PCIe Endpoint driver and binding

Add MAINTAINERS entry for Qualcomm PCIe Endpoint driver and its devicetree
binding.  Also fix the PCIe RC entry to cover only the RC driver.

Link: https://lore.kernel.org/r/20210920065946.15090-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>