There were multiple bugs in the OPAL RTC code which had never been
discovered, as the default configuration of OPAL machines is to
have the BMC / FSP control the RTC.
* Fix calling convention for setting the time -- the variables are passed
directly in CPU registers, not via memory.
* Fix bug in the bcd encoding routines. (from jhibbits)
Tested on POWER9 Talos II (BE) and POWER9 Blackbird (LE).
Reviewed by: jhibbits (in irc)
Sponsored by: Tag1 Consulting, Inc.
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