AmpereAltraPkg: Add Hot Plug Slot Capable during PCIe port initialization

In order to detect the NVMe after OS boots successfully but that NVMe's
not present previously. Hot Plug Slot Capable will help PCI Linux driver
to initialize its slot iomem resource which is used for detecting the
disk when it's inserted.

Signed-off-by: Minh Nguyen <minhnguyen1@os.amperecomputing.com>