Add API for available GPU memory

Add support for AMD Agent to return amount of memory available

Change-Id: I5c32e2cebbaa2993b044250aefe434e4cc02d8c2
Signed-off-by: David Yat Sin <david.yatsin@amd.com>

runtime/hsa-runtime/core/util/simple_heap.h

@@ -282,6 +282,8 @@ template <typename Allocator> class SimpleHeap {
     cache_size_ = 0;
   }
 
+  size_t cache_size() const { return cache_size_; }
+
   size_t default_block_size() const { return block_allocator_.block_size(); }
 
   // Prevent reuse of the block containing ptr.  No further fragments will be allocated from the