firewire: add CSR PRIORITY_BUDGET support

If supported by the OHCI controller, implement the PRIORITY_BUDGET
register, which is required for nodes that can use asynchronous
priority arbitration.

To allow the core to determine what features the lowlevel device
supports, add a new card driver callback.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index cdf8213..a50377d 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -32,6 +32,7 @@
 #define CSR_CYCLE_TIME			0x200
 #define CSR_BUS_TIME			0x204
 #define CSR_BUSY_TIMEOUT		0x210
+#define CSR_PRIORITY_BUDGET		0x218
 #define CSR_BUS_MANAGER_ID		0x21c
 #define CSR_BANDWIDTH_AVAILABLE		0x220
 #define CSR_CHANNELS_AVAILABLE		0x224