+ * This function initializes the PF/SM mailbox for use. It will split the
+ * buffer provided and use that to populate both the Tx and Rx FIFO by
+ * evenly splitting it. In order to allow for easy masking of head/tail
+ * the value reported in size must be a power of 2 and is reported in
+ * DWORDs, not bytes. Any invalid values will cause the mailbox to return
+ * error.