MIPS: Malta: Select 32bit DMA zone for 64-bit kernels

Enable the 32-bit DMA zone for 64-bit Malta kernels so that devices with
32-bit coherent DMA masks aren't constrained to the low 16MB DMA zone,
which can easily be exhausted when there is lots of static kernel data
due to lock and RCU debugging.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9890/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -440,6 +440,7 @@ config MIPS_MALTA
 	select SYS_SUPPORTS_MULTITHREADING
 	select SYS_SUPPORTS_SMARTMIPS
 	select SYS_SUPPORTS_ZBOOT
+	select ZONE_DMA32 if 64BIT
 	help
 	  This enables support for the MIPS Technologies Malta evaluation
 	  board.