Now that we have common definitions for SMCCC conduits, move the SDEI
code over to them, and remove the SDEI-specific definitions.

There should be no functional change as a result of this patch.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Acked-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: NJames Morse <james.morse@arm.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>