Simplify rtsx_comm_set_aspm() and remove the now-unused
rtsx_pci_enable_aspm().

rtsx_pci_disable_aspm() is still used by rtsx_pci_init_hw().
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20200521180545.1159896-6-helgaas@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>