PCI: brcmstb: Add suspend and resume pm_ops

Broadcom Set-top (BrcmSTB) boards typically support S2, S3, and S5 suspend
and resume.  Now the PCIe driver may do so as well.

Link: https://lore.kernel.org/r/20200911175232.19016-5-james.quinlan@broadcom.com


Signed-off-by: Jim Quinlan <jquinlan@broadcom.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>