When the Memory Tagging Extension is enabled, the tags need to be
preserved across page copy (e.g. for copy-on-write, page migration).

Introduce MTE-aware copy_{user_,}highpage() functions to copy tags to
the destination if the source page has the PG_mte_tagged flag set.
copy_user_page() does not need to handle tag copying since, with this
patch, it is only called by the DAX code where there is no source page
structure (and no source tags).
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>