Implement sceVdecCoreQueryInstanceSize, sceVdecCoreQueryFrameBufferInfo,
sceVdecCoreQueryComputeResourceInfo, sceVdecCoreCreateDecoder,
sceVdecCoreDeleteDecoder and sceVdecCoreMapMemoryBlock as shadPS4's
vdeccore.cpp does at 0614ce324b: its argument and codec-type checks, its
1920x1080 and 16-frame defaults, DPB counts from -1 to 16, its instance,
compute and frame-buffer sizes, and frame-buffer slots cut from mapped
blocks.
CreateDecoder opens an FFmpeg H.264 or HEVC context with the FFmpeg the
tree already links for libSceVideodec2 but starts no decode thread. The
library gets its own CMakeLists.txt and a guest_vdec_core test.
Dean