microblaze: trivial: Add comment for AXI pvr

AXI and OPB share some PVR macros.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/include/asm/pvr.h

@@ -39,9 +39,9 @@ struct pvr_s {
 #define PVR1_USER2_MASK			0xFFFFFFFF
 
 /* Configuration PVR masks */
-#define PVR2_D_OPB_MASK			0x80000000
+#define PVR2_D_OPB_MASK			0x80000000 /* or AXI */
 #define PVR2_D_LMB_MASK			0x40000000
-#define PVR2_I_OPB_MASK			0x20000000
+#define PVR2_I_OPB_MASK			0x20000000 /* or AXI */
 #define PVR2_I_LMB_MASK			0x10000000
 #define PVR2_INTERRUPT_IS_EDGE_MASK	0x08000000
 #define PVR2_EDGE_IS_POSITIVE_MASK	0x04000000
@@ -64,8 +64,8 @@ struct pvr_s {
 #define PVR2_OPCODE_0x0_ILL_MASK	0x00000040
 #define PVR2_UNALIGNED_EXC_MASK		0x00000020
 #define PVR2_ILL_OPCODE_EXC_MASK	0x00000010
-#define PVR2_IOPB_BUS_EXC_MASK		0x00000008
-#define PVR2_DOPB_BUS_EXC_MASK		0x00000004
+#define PVR2_IOPB_BUS_EXC_MASK		0x00000008 /* or AXI */
+#define PVR2_DOPB_BUS_EXC_MASK		0x00000004 /* or AXI */
 #define PVR2_DIV_ZERO_EXC_MASK		0x00000002
 #define PVR2_FPU_EXC_MASK		0x00000001