Vulkan: Bugfixes in preferGlobalPipelineCache 1. per-program pipeline cache was being unconditionally initialized during warmup 2. mergeProgramPipelineCachesToGlobalCache should be disabled when preferGlobalPipelineCache feature is enabled Also, prefer use of global pipeline cache for Samsung. Bug: angleproject:386749841 Change-Id: Ifd66ef8c6d10b8a5ffd3c002239e8747f469ba47 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6936119 Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: mohan maiya <m.maiya@samsung.com>