arm64: smp: Harden parallel CPU bringup against broken PSCI firmware

Since firmware has occasionally been known to get things wrong, harden
our parallel CPU bringup code against a PSCI implementation that passes
the CPU_ON argument to an incorrect CPU.

The primary CPU writes the MPIDR of the incoming CPU to the end of its
task stack and this is then checked against the MPIDR_EL1 register
during early kernel entry. A mismatch is reported via the existing
failure reporting mechanism and the CPU is not brought online.

Suggested-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Will Deacon <will@kernel.org>