arm: add SMCCC protocol definitions

arm: add SMCCC protocol definitions

Add generic definitions used in ARM SMC call convention.
Those definitions was originally added to Linux kernel as
include/linux/arm-smccc.h by commit 98dd64f34f47
("ARM: 8478/2: arm/arm64: add arm-smccc")

I extended them and formatted according to XEN coding style. Some
of the macros were converted to inlined functions to ease parsing.

They can be used by both SMCCC clients (like PSCI) and by SMCCC
servers (like vPSCI or upcoming generic SMCCC handler).

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>