platform/mellanox: mlxreg-io: Add locking for io operations

Add lock to protect user read/write access to the registers.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20220711084559.62447-8-vadimp@nvidia.com


Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>