[MIPS] Delete unused CONFIG_DMA_IP32.

The functionality of the former dma-ip32.c has been folded into
dma-default.c.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -797,10 +797,6 @@ config DMA_COHERENT
 config DMA_IP27
 	bool
 
-config DMA_IP32
-	bool
-	select DMA_NEED_PCI_MAP_STATE
-
 config DMA_NONCOHERENT
 	bool
 	select DMA_NEED_PCI_MAP_STATE