arm64: Fix behavior of maxcpus=N

arm64: Fix behavior of maxcpus=N

maxcpu=n sets the number of CPUs activated at boot time to a max of n,
but allowing the remaining CPUs to be brought up later if the user
decides to do so. However, on arm64 due to various reasons, we disallowed
hotplugging CPUs beyond n, by marking them not present. Now that
we have checks in place to make sure the hotplugged CPUs have compatible
features with system and requires no new errata, relax the restriction.

Cc: Will Deacon <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: James Morse <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Signed-off-by: Suzuki K Poulose <[email protected]>
Signed-off-by: Will Deacon <[email protected]>