iommu: iommu-debug: Include map_sg dma api functional test

Allow testing of basic dma_{map/unmap}_sg functionality as
part of the arm dma api test suite.

Also, currently each sg list points to the same page being
allocated. Make the spectrum of testing sg mappings more wider
by pointing each sg list to different pages being allocated.

Change-Id: Ic3a1e78cf6e87093fd95aa3b8ee8a7bdd38092b7
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>