stm class: Support devices that override software assigned masters

Some STM devices adjust software assigned master numbers depending on
the trace source and its runtime state and whatnot. This patch adds
a sysfs attribute to inform the trace-side software that master numbers
assigned to software sources will not match those in the STP stream,
so that, for example, master/channel allocation policy can be adjusted
accordingly.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-class-stm

@@ -12,3 +12,13 @@ KernelVersion:	4.3
 Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
 Description:
 		Shows the number of channels per master on this STM device.
+
+What:		/sys/class/stm/<stm>/hw_override
+Date:		March 2016
+KernelVersion:	4.7
+Contact:	Alexander Shishkin <alexander.shishkin@linux.intel.com>
+Description:
+		Reads as 0 if master numbers in the STP stream produced by
+		this stm device will match the master numbers assigned by
+		the software or 1 if the stm hardware overrides software
+		assigned masters.