arm/arm64: Provide a wrapper for SMCCC 1.1 calls

SMCCC 1.1 calls may use either HVC or SMC depending on the PSCI
conduit. Rather than coding this in every call site provide a macro
which uses the correct instruction. The macro also handles the case
where no PSCI conduit is configured returning a not supported error
in res, along with returning the conduit used for the call.

This allow us to remove some duplicated code and will be useful later
when adding paravirtualized time hypervisor calls.

Signed-off-by: Steven Price <steven.price@arm.com>