Tegra186: remove ENABLE_AFI_DEVICE macro usage

This patch removes this macro and its usage as it is used only
within the Tegra186 files and all derived platforms keep the
macro enabled.

Change-Id: Ib831b3c002ba4dedc3d5fafbb7d321daa28fa9ea
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>