imgtec/pistachio: Add SOC_REGISTERS memory region

When used with a U-boot payload it will need this region
identity mapped also, so we're defining it in preparation
for that functionality.

Change-Id: I27cee5b58cb899433b52bd06df07b5f2105212af
Signed-off-by: Ionela Voinescu <ionela.voinescu@imgtec.com>
Reviewed-on: https://review.coreboot.org/12768
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>

src/arch/mips/include/arch/memlayout.h

@@ -26,4 +26,6 @@
 
 #define DMA_COHERENT(addr, size) REGION(dma_coherent, addr, size, 4K)
 
+#define SOC_REGISTERS(addr, size) REGION(soc_registers, addr, size, 4)
+
 #endif /* __ARCH_MEMLAYOUT_H */