Check that the OPAL_RTC_READ token exists before we use the OPAL RTC.
Refactors the code a little to merge error paths.
This avoids littering the OPAL console with:
"OPAL: Called with bad token 3".
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>