wrapper for clEnqueueSVMMemFill and clEnqueueSVMMemcpy

[bananAshkar]

1. SVMAllocator::allocate automatically maps the newly allocated SVM buffer. This is redundant for output buffers.I added a new argument to the method – bool map = true – to control whether the method should map the buffer.

2.opencl.hpp doesn't include wrapper methods for clEnqueueSVMMemFill and clEnqueueSVMMemcpy , so I added them.

[CLAassistant]

All committers have signed the CLA.

[bashbaug]

Merging as discussed in the May 30th teleconference.