[CORE] Extend heap APIs to ease heap creation, and create DMA heap.

This patch modifies heap APIs to ease heap creation, and creates DMA heap in
addtion to normal heap. Now, drivers can allocate dmable memory using
vmm_dma_malloc, and free using vmm_dma_free.

Signed-off-by: Ankit Jindal <thatsjindal@gmail.com>
Signed-off-by: Anup Patel <anup@brainfault.org>