arm64: mte: Check the DT memory nodes for MTE support

Even if the ID_AA64PFR1_EL1 register advertises the presence of MTE, it
is not guaranteed that the memory system on the SoC supports the
feature. In the absence of system-wide MTE support, the behaviour is
undefined and the kernel should not enable the MTE memory type in
MAIR_EL1.

For FDT, add an 'arm,armv8.5-memtag' property to the /memory nodes and
check for its presence during MTE probing. For example:

	memory@80000000 {
		device_type = "memory";
		arm,armv8.5-memtag;
		reg = <0x00000000 0x80000000 0 0x80000000>,
		      <0x00000008 0x80000000 0 0x80000000>;
	};

If the /memory nodes are not present in DT or if at least one node does
not support MTE, the feature will be disabled. On EFI systems, it is
assumed that the memory description matches the EFI memory map (if not,
it is considered a firmware bug).

MTE is not currently supported on ACPI systems.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Rob Herring <Rob.Herring@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>