arm64: update ASID limit

During a rollover, we mark the active ASID on each CPU as reserved, before
allocating a new ID for the task that caused the rollover. This means that
with N CPUs, we can only guarantee the new task to obtain a valid ASID if
we have at least N+1 ASIDs. Update this limit in the initcall check.

Note that this restriction was introduced by commit 8e648066 on the
arch/arm side, which disallow re-using the previously active ASID on the
local CPU, as it would introduce a TLB race.

In addition, we only dispose of NUM_USER_ASIDS-1, since ASID 0 is
reserved. Add this restriction as well.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>