ARM: 8307/1: psci: move psci firmware calls out of line

arm64 builds with GCC 5 have caused the __asmeq assertions in the PSCI
calling code to fire, so move the ARM PSCI calls out of line into their
own assembly file for consistency and to safeguard against the same
issue occuring with the 32-bit toolchain.

[will: brought into line with arm64 implementation]

Reported-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>