arch_topology: Make cpu_capacity sysfs node as read-only

If user updates any cpu's cpu_capacity, then the new value is going to
be applied to all its online sibling cpus. But this need not to be correct
always, as sibling cpus (in ARM, same micro architecture cpus) would have
different cpu_capacity with different performance characteristics.
So, updating the user supplied cpu_capacity to all cpu siblings
is not correct.

And another problem is, current code assumes that 'all cpus in a cluster
or with same package_id (core_siblings), would have same cpu_capacity'.
But with commit '5bdd2b3f

 ("arm64: topology: add support to remove
cpu topology sibling masks")', when a cpu hotplugged out, the cpu
information gets cleared in its sibling cpus. So, user supplied
cpu_capacity would be applied to only online sibling cpus at the time.
After that, if any cpu hotplugged in, it would have different cpu_capacity
than its siblings, which breaks the above assumption.

So, instead of mucking around the core sibling mask for user supplied
value, use device-tree to set cpu capacity. And make the cpu_capacity
node as read-only to know the asymmetry between cpus in the system.
While at it, remove cpu_scale_mutex usage, which used for sysfs write
protection.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Quentin Perret <quentin.perret@arm.com>
Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>