spapr: Don't use weird units for MIN_RMA_SLOF

MIN_RMA_SLOF records the minimum about of RMA that the SLOF firmware
requires.  It lets us give a meaningful error if the RMA ends up too small,
rather than just letting SLOF crash.

It's currently stored as a number of megabytes, which is strange for global
constants.  Move that megabyte scaling into the definition of the constant
like most other things use.

Change from M to MiB in the associated message while we're at it.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

hw/ppc/spapr.c

@@ -103,7 +103,7 @@
 #define FW_OVERHEAD             0x2800000
 #define KERNEL_LOAD_ADDR        FW_MAX_SIZE
 
-#define MIN_RMA_SLOF            128UL
+#define MIN_RMA_SLOF            (128 * MiB)
 
 #define PHANDLE_INTC            0x00001111
 
@@ -2956,10 +2956,10 @@ static void spapr_machine_init(MachineState *machine)
         }
     }
 
-    if (spapr->rma_size < (MIN_RMA_SLOF * MiB)) {
+    if (spapr->rma_size < MIN_RMA_SLOF) {
         error_report(
-            "pSeries SLOF firmware requires >= %ldM guest RMA (Real Mode Area memory)",
-            MIN_RMA_SLOF);
+            "pSeries SLOF firmware requires >= %ldMiB guest RMA (Real Mode Area memory)",
+            MIN_RMA_SLOF / MiB);
         exit(1);
     }