platform: tegra: nvadsp: Detect simulation with DT

platform: tegra: nvadsp: Detect simulation with DT

Adding ADSP DT attribute "nvidia,adsp_unit_fpga" which can be used
detect if adsp is running on Unit-FPGA or on actual silicon.

Bug 200081122

Change-Id: Ie0aa568f63df172315712421acfbf439f6417ed8
Signed-off-by: Ajay Nandakumar <anandakumarm@nvidia.com>
Reviewed-on: http://git-master/r/712313
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Nitin Kumbhar <nkumbhar@nvidia.com>
Tested-by: Nitin Kumbhar <nkumbhar@nvidia.com>