pci: msm: Use endpoint list to track suspend and resume

Decouple endpoint event registration from link suspend.
Instead of relying on pending_ep_reg and num_active_ep
create an enumerated endpoint list at the time of endpoint
enumeration and move it to suspended endpoint list up
on link suspend. If enumerated endpoint list becomes
empty allow link suspend. Move endpoint back to enumerated
list upon resume. This also removes a race where all
endpoints have not completed their enumeration and one of
the endpoints request to suspend the link.

Change-Id: I22ac6e52a4c93d294d2a365da63cc7292e5e36ce
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>