This patch will unblock SYNCHRONIZE_CACHE command to firmware, i.e. don't block the SYNCHRONIZE_CACHE command at driver instead of
passing it to firmware for all Gen3 controllers.
For Thunderbolt controller, keep the legacy behavior i.e. return the SYNCHRONIZE_CACHE command with success status from driver itself.

There is Sysctl parameter 'block_sync_cache' is provided to enable customers either to block/unblock these commands to facilitate
legacy behavior if there is a compatibility issue. Default value for module parameter is to unblock this command.

Submitted by: Sumit Saxena <sumit.saxena@broadcom.com>
Reviewed by: Kashyap Desai <Kashyap.Desai@broadcom.com>
MFC after: 3 days
Sponsored by: Broadcom Limited/AVAGO Technologies