Add legacy-align parameter to DmabufHeapAlloc()

The parameter is intended to make the API backwards compatible with
legacy ION devices. It will be ignored for devices that support DMA-BUF
heaps.

Test: build
Bug: 154310076
Change-Id: Ic5b49269283caa7d05d9468f8ed7f02e1b3c1f1e
Merged-In: Ic5b49269283caa7d05d9468f8ed7f02e1b3c1f1e