[Ozone] Update GYP and GN to include a DRM platform

This makes it possible to refer to the platform as DRI and DRM. We need
this intermediate state so we can update the CrOS builds to use DRM
rather than DRI.

BUG=none
TEST=Build ozone with DRI & DRM platform and without to verify build
(GYP and GN)

Review URL: https://codereview.chromium.org/957253005

Cr-Original-Commit-Position: refs/heads/master@{#320788}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d89b572673f0fd352ae9d14e69b79e0430c87fbd

common.gypi

@@ -1497,6 +1497,7 @@
     # Ozone platforms to include in the build.
     'ozone_platform_caca%': 0,
     'ozone_platform_dri%': 0,
+    'ozone_platform_drm%': 0,
     'ozone_platform_egltest%': 0,
     'ozone_platform_gbm%': 0,
     'ozone_platform_ozonex%': 0,
@@ -2347,6 +2348,7 @@
         # Build all platforms whose deps are in install-build-deps.sh.
         # Only these platforms will be compile tested by buildbots.
         'ozone_platform_dri%': 1,
+        'ozone_platform_drm%': 1,
         'ozone_platform_test%': 1,
         'ozone_platform_egltest%': 1,
       }],

filename_rules.gypi

@@ -106,11 +106,6 @@
                     ['exclude', '(^|/)evdev/'],
       ]
     }],
-    ['<(ozone_platform_dri)==0 or >(nacl_untrusted_build)==1', {
-      'sources/': [ ['exclude', '_dri(_browsertest|_unittest)?\\.(h|cc)$'],
-                    ['exclude', '(^|/)dri/'],
-      ]
-    }],
     ['<(use_pango)==0', {
       'sources/': [ ['exclude', '(^|_)pango(_util|_browsertest|_unittest)?\\.(h|cc)$'], ],
     }],

linux/system.gyp

@@ -508,7 +508,7 @@
         },
       ],
     }],
-    ['ozone_platform_dri==1 or ozone_platform_gbm==1', {
+    ['ozone_platform_dri==1 or ozone_platform_drm==1 or ozone_platform_gbm==1', {
       'targets': [
         {
           'target_name': 'libdrm',