arm64: cpuinfo: print info for all CPUs

Currently reading /proc/cpuinfo will result in information being read
out of the MIDR_EL1 of the current CPU, and the information is not
associated with any particular logical CPU number.

This is problematic for systems with heterogeneous CPUs (i.e.
big.LITTLE) where MIDR fields will vary across CPUs, and the output will
differ depending on the executing CPU.

This patch reorganises the code responsible for /proc/cpuinfo to print
information per-cpu. In the process, we perform several cleanups:

* Property names are coerced to lower-case (to match "processor" as per
  glibc's expectations).
* Property names are simplified and made to match the MIDR field names.
* Revision is changed to hex as with every other field.
* The meaningless Architecture property is removed.
* The ripe-for-abuse Machine field is removed.

The features field (a human-readable representation of the hwcaps)
remains printed once, as this is expected to remain in use as the
globally support CPU features. To enable the possibility of the addition
of per-cpu HW feature information later, this is printed before any
CPU-specific information.

Comments are added to guide userspace developers in the right direction
(using the hwcaps provided in auxval). Hopefully where userspace
applications parse /proc/cpuinfo rather than using the readily available
hwcaps, they limit themselves to reading said first line.

If CPU features differ from each other, the previously installed sanity
checks will give us some advance notice with warnings and
TAINT_CPU_OUT_OF_SPEC. If we are lucky, we will never see such systems.
Rework will be required in many places to support such systems anyway.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marcus Shawcroft <marcus.shawcroft@arm.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
[catalin.marinas@arm.com: remove machine_name as it is no longer reported]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>