xilinx_spips: Add automatic start support

SPI has a mode where it automatically starts based on tx fifo
occupancy. Implemented.
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NEdgar E. Iglesias <edgar.iglesias@gmail.com>
Message-id: f4e9accb5de87b526fff6ed937f63278db76533b.1369117359.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/ssi/xilinx_spips.c

@@ -451,7 +451,8 @@ static void xilinx_spips_write(void *opaque, hwaddr addr,
     }
     s->regs[addr] = (s->regs[addr] & ~mask) | (value & mask);
 no_reg_update:
-    if (man_start_com) {
+    if ((man_start_com && s->regs[R_CONFIG] & MAN_START_EN) ||
+            (fifo8_is_empty(&s->tx_fifo) && s->regs[R_CONFIG] & MAN_START_EN)) {
         xilinx_spips_flush_txfifo(s);
     }
     xilinx_spips_update_ixr(s);