Atomic: Add missing defines in GYP files
Atomic: Add missing defines in GYP files

InitializeGPU in OzonePlatformGBM, will set use_atomic flag to true
in case USE_DRM_ATOMIC is enabled. Currently, we never set this due to
missing define in gbm.gypi file

BUG=370522

Review URL: https://codereview.chromium.org/1306773004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#347018}

Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,Chilledheart/chromium