msm/gpu/a6xx: Force of_dma_configure to setup DMA for GMU

The point of the 'force_dma' parameter for of_dma_configure
is to force the device to be set up even if DMA capability is
not described by the firmware which is exactly the use case
 we have for GMU - we need SMMU to get set up but we have no
other dma capabilities since memory is managed by the GPU
driver. Currently we pass false so of_dma_configure() fails
and subsequently GMU and GPU probe does as well.

Fixes: 4b565ca5 ("drm/msm: Add A6XX device support")
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Tested-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>