Use monotonic raw timestamp by default except for x86/64

use_alsa_monotonic_raw_tstamps flag should be set to true for
all audio products since alsa-lib is upgraded to 1.0.29 which
added monotonic raw timestamp feature. Setting it to true so
we don't need to add this flag to every internal audio targets
and C4A partners.

BUG=internal b/27654854
TEST=build pepperoni and make sure snd_pcm_sw_params_set_tstamp_type
  is called.

Review URL: https://codereview.chromium.org/1804763002

Cr-Commit-Position: refs/heads/master@{#381534}

chromecast/media/cma/backend/alsa/BUILD.gn

@@ -3,13 +3,14 @@
 # found in the LICENSE file.
 
 import("//build/buildflag_header.gni")
+import("//build/config/chromecast_build.gni")
 import("//media/media_options.gni")
 import("//testing/test.gni")
 
 declare_args() {
-  # Set true to use raw timestamps. This should only be enabled when the ALSA
-  # library supports it.
-  use_alsa_monotonic_raw_tstamps = false
+  # Set true to use raw timestamps on non-desktop cast build.
+  # ALSA version equal or later than 1.0.29 support this function.
+  use_alsa_monotonic_raw_tstamps = !is_cast_desktop_build
 }
 
 # Alsa must be used for these targets to build.