gpu: ion: Add flag for forcing contiguous allocations

Previously, a parameter was added to secure heaps to only
allow secure allocations. Some clients still require
non-secure contiguous allocations even though the SMMU is
supported. Add support for those clients to force contiguous
allocations to go through.

Change-Id: I0d18d8a9ed3ab267b55c84c4ad160f8cec2c2b32
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>