arm64: mte: Fast track reserving tag storage when the block is free

A double digit performance decrease for Chrome startup time has been
reported with the dynamic tag storage management enabled. A large part of
the regression is due to lru_cache_disable(), called from
__alloc_contig_migrate_range(), which IPIs all CPUs in the system.

Improve the performance by taking the storage block directly from the
freelist if it's free, thus sidestepping the costly function call.

Note that at the moment this is implemented only when the block size is
1 (the block is one page); larger block sizes could be added later if
necessary.