Refactor registered memory calls.

include/hip/hcc_detail/hip_runtime_api.h

@@ -858,6 +858,8 @@ hipError_t hipPointerGetAttributes(hipPointerAttribute_t *attributes, void* ptr)
  *  @param[out] ptr Pointer to the allocated memory
  *  @param[in]  size Requested memory size
  *
+ *  If size is 0, no memory is allocated, *ptr returns nullptr, and hipSuccess is returned.
+ *
  *  @return #hipSuccess
  *
  *  @see hipMallocPitch, hipFree, hipMallocArray, hipFreeArray, hipMalloc3D, hipMalloc3DArray, hipHostFree, hipHostMalloc
@@ -870,6 +872,8 @@ hipError_t hipMalloc(void** ptr, size_t size) ;
  *  @param[out] ptr Pointer to the allocated host pinned memory
  *  @param[in]  size Requested memory size
  *
+ *  If size is 0, no memory is allocated, *ptr returns nullptr, and hipSuccess is returned.
+ *
  *  @return #hipSuccess, #hipErrorMemoryAllocation
  *
  *  @deprecated use hipHostMalloc() instead
@@ -883,6 +887,8 @@ hipError_t hipMallocHost(void** ptr, size_t size) __attribute__((deprecated("use
  *  @param[in]  size Requested memory size
  *  @param[in]  flags Type of host memory allocation
  *
+ *  If size is 0, no memory is allocated, *ptr returns nullptr, and hipSuccess is returned.
+ *
  *  @return #hipSuccess, #hipErrorMemoryAllocation
  *
  *  @see hipSetDeviceFlags, hipHostFree
@@ -896,6 +902,8 @@ hipError_t hipHostMalloc(void** ptr, size_t size, unsigned int flags) ;
  *  @param[in]  size Requested memory size
  *  @param[in]  flags Type of host memory allocation
  *
+ *  If size is 0, no memory is allocated, *ptr returns nullptr, and hipSuccess is returned.
+ *
  *  @return #hipSuccess, #hipErrorMemoryAllocation
  *
  *  @deprecated use hipHostMalloc() instead
@@ -980,6 +988,9 @@ hipError_t hipHostUnregister(void* hostPtr) ;
  *  @param[out] pitch Pitch for allocation (in bytes)
  *  @param[in]  width Requested pitched allocation width (in bytes)
  *  @param[in]  height Requested pitched allocation height
+ *
+ *  If size is 0, no memory is allocated, *ptr returns nullptr, and hipSuccess is returned.
+ *
  *  @return Error code
  *
  *  @see hipMalloc, hipFree, hipMallocArray, hipFreeArray, hipHostFree, hipMalloc3D, hipMalloc3DArray, hipHostMalloc