devicetree.bbclass: Combine stderr into stdout to see actual dtc error

Previously the subprocess command to run dtc was not properly displaying
the error on console. Combining stderr into stdout for the dtc subprocess
so the actual error can be seen on console without having to open the
do_compile log.

For example, previously on a dtc error, just the following stack trace
and dtc command was being shown on console:

File: 'exec_python_func() autogenerated', lineno: 2, function: <module>
     0001:
 *** 0002:devicetree_do_compile(d)
     0003:
File:
function: devicetree_do_compile
     0127:            if not(os.path.isfile(dtspath)) or
not(dts.endswith(".dts") or devicetree_source_is_overlay(dtspath)):
     0128:                continue # skip non-.dts files and non-overlay
files
     0129:        except:
     0130:            continue # skip if can't determine if overlay
 *** 0131:        devicetree_compile(dtspath, includes, d)

    ...

Exception: subprocess.CalledProcessError: Command '['dtc', '-R', '8',
'-b', '0', '-p', '0x1000', '-i', '${INCLUDES}, '-o', 'system-top.dtb',
'-I', 'dts', '-O', 'dtb', 'system-top.dts.pp']' returned non-zero exit
status 1

with this patch, the actual error from the dtc command will be appended
like the following:

Subprocess output:
Error: Label or path not found
FATAL ERROR: Syntax error parsing input tree

Signed-off-by: Jaewon Lee <jaewon.lee@xilinx.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/meta/classes/devicetree.bbclass b/meta/classes/devicetree.bbclass
index 5c03e4b0fd..d8779c7943 100644
--- a/meta/classes/devicetree.bbclass
+++ b/meta/classes/devicetree.bbclass
@@ -116,7 +116,7 @@ def devicetree_compile(dtspath, includes, d):
     dtcargs += ["-o", "{0}.{1}".format(dtname, "dtbo" if isoverlay else "dtb")]
     dtcargs += ["-I", "dts", "-O", "dtb", "{0}.pp".format(dts)]
     bb.note("Running {0}".format(" ".join(dtcargs)))
-    subprocess.run(dtcargs, check = True)
+    subprocess.run(dtcargs, check = True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
 
 python devicetree_do_compile() {
     includes = expand_includes("DT_INCLUDE", d)