OPAL_GET_MSG
------------

OPAL_GET_MSG will get the next pending OPAL Message (see
opal-messages.txt).

Parameters:
	buffer to copy message into
	sizeof buffer to copy message into

The maximum size of an opal message is specified in the device tree passed
to the host OS:

  ibm,opal {
            opal-msg-size = <0x48>;
  }

It is ALWAYS at least 72 bytes. In the future, OPAL may have messages larger
than 72 bytes. Naturally, a HOST OS will only be able to interpret these
if it correctly uses opal-msg-size. Any OPAL message > 72 bytes, a host OS
may safely ignore.

A host OS *SHOULD* always supply a buffer to OPAL_GET_MSG of either 72
bytes or opal-msg-size. It MUST NOT supply a buffer of < 72 bytes.


Return values:

OPAL_RESOURCE - no available message.

OPAL_PARAMETER - buffer is NULL or size is < 72 bytes.
	         If buffer size < 72 bytes, the message will NOT be discarded
		 by OPAL.

OPAL_PARTIAL - If pending opal message is greater than supplied buffer.
               In this case the message is *DISCARDED* by OPAL.
	       This is to keep compatibility with host Operating Systems
	       with a hard coded opal-msg-size of 72 bytes.
	       NOT CURRENTLY IMPLEMENTED. Specified so that host OS can
	       prepare for the possible future with either a sensible
	       error message or by gracefully ignoring such OPAL messages.

OPAL_SUCCESS - message successfully copied to buffer.