Move linux pkg_config() calls into separate BUILD.gn files

This showed up as a bottleneck for gn gen on Android. Refactoring these
out improves gn gen time (avg of 3 trails on my machine) from 2151->1984

BUG=none

Review URL: https://codereview.chromium.org/1909273002

Cr-Commit-Position: refs/heads/master@{#389484}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index d182216..d153f91e 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -876,7 +876,7 @@
 
   if (is_linux) {
     if (use_aura) {
-      configs += [ "//build/config/linux:dbus" ]
+      configs += [ "//build/config/linux/dbus" ]
       deps += [
         "//build/linux:fontconfig",
         "//dbus",
@@ -1233,7 +1233,7 @@
       "chromeos/system/fake_input_device_settings.cc",
       "chromeos/system/fake_input_device_settings.h",
     ]
-    configs += [ "//build/config/linux:dbus" ]
+    configs += [ "//build/config/linux/dbus" ]
     deps += [ "//chromeos:test_support" ]
   }