tracing/blktrace: move the tracing file to kernel/trace, fix

Impact: build fix

The BLK_DEV_IO_TRACE entry used to be in block/Kconfig - which
file itself was dependent on CONFIG_BLOCK. But now the entry is
in kernel/trace/Kconfig - which is present even on !CONFIG_BLOCK.

So add a 'depends on BLOCK' to BLK_DEV_IO_TRACE.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/Kconfig

@@ -305,6 +305,7 @@ config WORKQUEUE_TRACER
 config BLK_DEV_IO_TRACE
 	bool "Support for tracing block io actions"
 	depends on SYSFS
+	depends on BLOCK
 	select RELAY
 	select DEBUG_FS
 	select TRACEPOINTS