MIPS: Generic: Fix big endian CPUs on generic machine

Big endian CPUs require SWAP_IO_SPACE enabled to swap accesses to little
endian peripherals.

Without this patch, big endian kernels fail to communicate with little
endian periperals, such as PCI devices, on QEMU and FPGA based
platforms.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Fixes: eed0eabd12ef ("MIPS: generic: Introduce generic DT-based board support")
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/15105/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -97,6 +97,7 @@ config MIPS_GENERIC
 	select PCI_DRIVERS_GENERIC
 	select PINCTRL
 	select SMP_UP if SMP
+	select SWAP_IO_SPACE
 	select SYS_HAS_CPU_MIPS32_R1
 	select SYS_HAS_CPU_MIPS32_R2
 	select SYS_HAS_CPU_MIPS32_R6