Function identifiers are a 32bit, unsigned quantity. But we never
tell so to the compiler, resulting in the following:

 4ac:   b26187e0        mov     x0, #0xffffffff80000001

We thus rely on the firmware narrowing it for us, which is not
always a reasonable expectation.

Cc: stable@vger.kernel.org
Reported-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: NRobin Murphy <robin.murphy@arm.com>
Tested-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>