Add support for FF-A driver changes in v6.1

The in-kernel interface of the FF-A driver has changed with the v6.1
kernel release. The FF-A operations are now split into multiple groups,
and instead of using the ffa_dev_ops_get() function now the ops struct
can be reached directly.

This patch introduces wrapper functions around the FF-A operations to
enable using the new in-kernel interface in a backwards compatible way.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: I2a223a2e079d9afc693da629fad462eb9d95b3a3