arm64: Add architecture specific ACPI FFH Opregion callbacks

FFH Operation Region space can be used to trigger SMC or HVC calls,
using the Arm SMC Calling Convention (SMCCC). The choice of conduit
(SMC or HVC) is based on what the kernel choose based on PSCI as with
any other users of SMCCC within the kernel.

Function identifiers only in the SMCCC SiP Service, OEM Service and FF-A
specific call range are allowed in FFH Opregions.

Offset can be either 0(32 bit calling convention) or 1(64 bit calling
convention). The length must be set with the range applicable based
on the value of the offset.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>