2014-07-24  Sharath Kamath  <s.kamath@samsung.com>

        Enable the KHR_FP64 extension.

        In OpenCL1.2 only when CL_DEVICE_DOUBLE_FP_CONFIG is non-null the
        implementation supports double data type.
        Adopting the same in cacheExtensionsForDevice() to cache KHR_FP64 support.

        Issue #536

        Reviewed by Antonio.

        * platform/ComputeExtensions.h:
        * platform/opencl/ComputeExtensionsCL.cpp:
        (WebCore::ComputeExtensions::supports):
        (WebCore::ComputeExtensions::supportsExtension):
        (WebCore::ComputeExtensions::cacheGlobalExtensions):
        (WebCore::ComputeExtensions::cacheExtensionsForDevice):
        (WebCore::ComputeExtensions::cacheExtensionsForPlatform):