kernarg buffer allocation strategy improvement

[scchan]

• add the capability to allocate kernarg buffer in coarse grained GPU memory to leverage caching (off by default)
• implemented a new algorithm to manage kernarg buffers
  • provides a control point when to recycle old kernel buffers (for coarse grained buffers)
  • more efficient free kernarg buffer lookup
  • supports multiple pools with kernarg buffer sizes

[scchan]

branch rebased and resolved conflicts