nvme-pci: Use host managed power state for suspend

nvme-pci: Use host managed power state for suspend

BugLink: https://bugs.launchpad.net/bugs/1808957
The nvme pci driver prepares its devices for power loss during suspend
by shutting down the controllers. The power setting is deferred to
pci driver's power management before the platform removes power. The
suspend-to-idle mode, however, does not remove power.

NVMe devices that implement host managed power settings can achieve
lower power and better transition latencies than using generic PCI power
settings. Try to use this feature if the platform is not involved with
the suspend. If successful, restore the previous power state on resume.

Cc: Mario Limonciello <Mario.Limonciello@dell.com>
Cc: Kai Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Mario Limonciello <mario.limonciello@dell.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
(backported from commit a0805317252ad9cf09d4a32b0435e165580adf8a git://git.infradead.org/nvme nvme-5.3)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Timo Aaltonen <tjaalton@ubuntu.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>