firmware: arm_ffa: Rename ffa_dev_ops as ffa_ops

firmware: arm_ffa: Rename ffa_dev_ops as ffa_ops

Except the message APIs, all other APIs are ffa_device independent and can
be used without any associated ffa_device from a non ffa_driver.

In order to reflect the same, just rename ffa_dev_ops as ffa_ops to
avoid any confusion or to keep it simple.

Link: https://lore.kernel.org/r/20220907145240.1683088-8-sudeep.holla@arm.com
Suggested-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>