platform/mellanox: mlxreg-hotplug: Use capability register for attribute creation

platform/mellanox: mlxreg-hotplug: Use capability register for attribute creation

Create the 'sysfs' attributes according to configuration provided
through the capability register, which purpose is to indicate the
actual number of the components within the particular group.
Such components could be, for example the FAN or power supply units.
The motivation is to avoid adding a new code in the future in order to
distinct between the systems types supporting a different number of the
components like power supplies, FANs, ASICs, line cards.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>