drivers/built-in.o: In function `ifx_spi_free_device':
ifx6x60.c:(.text+0x96d9a): undefined reference to `dma_free_coherent'
drivers/built-in.o: In function `ifx_spi_spi_probe':
ifx6x60.c:(.text+0x978a2): undefined reference to `dma_alloc_coherent'
While DMA is optional in this driver, and is used only if
ifx_modem_platform_data.use_dma is set, there are currently no in-tree
users of ifx_modem_platform_data (and thus of this driver), so just make
it depend on HAS_DMA.