gpci and 24x7 expose some device specific attributes. Add some
documentation for them.
Signed-off-by: NCody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>