dmaengine: tegra: explicitly select DMA_VIRTUAL_CHANNELS

dmaengine: tegra: explicitly select DMA_VIRTUAL_CHANNELS

Enabling TEGRA186_GPC_DMA will cause this build failure unless some other
DMA driver which uses DMA_VIRTUAL_CHANNELS is enabled:

  ERROR: modpost: "vchan_dma_desc_free_list" [drivers/dma/tegra186-gpc-dma.ko] undefined!
  ERROR: modpost: "vchan_init" [drivers/dma/tegra186-gpc-dma.ko] undefined!
  ERROR: modpost: "vchan_tx_submit" [drivers/dma/tegra186-gpc-dma.ko] undefined!
  ERROR: modpost: "vchan_tx_desc_free" [drivers/dma/tegra186-gpc-dma.ko] undefined!
  ERROR: modpost: "vchan_find_desc" [drivers/dma/tegra186-gpc-dma.ko] undefined!
  make[1]: *** [scripts/Makefile.modpost:136: Module.symvers] Error 1

Add an explicit select of DMA_VIRTUAL_CHANNELS to avoid this.

Signed-off-by: Mark Salter <msalter@redhat.com>
Link: https://lore.kernel.org/r/20230329172129.88403-1-msalter@redhat.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>