PCI: Add 32 GT/s decoding in some macros

Link speed 32.0 GT/s is supported in PCIe r5.0. Add this speed to
PCIE_SPEED2STR() and PCIE_SPEED2MBS_ENC() to correctly decode it.

This is complementary to de76cda2 ("PCI: Decode PCIe 32 GT/s link
speed").

Link: https://lore.kernel.org/r/1581937984-40353-2-git-send-email-yangyicong@hisilicon.com


Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>