Memory Tagging (part of the ARMv8.5 Extensions) provides
architectural support for run-time, always-on detection of
various classes of memory error to aid with software debugging
to eliminate vulnerabilities arising from memory-unsafe
languages.

This option enables the support for the Memory Tagging
Extension at EL0 (i.e. for userspace).

Selecting this option allows the feature to be detected at
runtime. Any secondary CPU not implementing this feature will
not be allowed a late bring-up.

Userspace binaries that want to use this feature must
explicitly opt in. The mechanism for the userspace is
described in:

Documentation/arm64/memory-tagging-extension.rst.