FROMLIST: arm64/mte: Document ABI for asymmetric mode

MTE3 adds a new mode which is synchronous for writes but asynchronous for
reads. Document the userspace ABI for this feature, we call the new mode
ASYMM and add a new prctl flag and mte_tcf_preferred value for it.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Link: https://lore.kernel.org/linux-arm-kernel/20220127195712.748150-2-broonie@kernel.org/


Change-Id: Iad3a5d23b59656072ca5962b2012d74adc1b210b
Bug: 217221156
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>