smccc: Define vendor hyp owned service call region

Vendor specific hypervisor services have their own region of function
identifiers reserved by SMCCC. Extend the list of owners to include this
case.

Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20200915104643.2543892-16-ascull@google.com