imgtec/pistachio: identity map SOC registers region

This region must be mapped uncached. This is necesary for an
U-boot payload which will obtain all register base addresses
as physical addresses from the device tree and will use them
as such.

Change-Id: Ib5041df7d90c6ef61b7448a18dd732afbd9489ca
Signed-off-by: Ionela Voinescu <ionela.voinescu@imgtec.com>
Reviewed-on: https://review.coreboot.org/12770
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/soc/imgtec/pistachio/bootblock.c

@@ -57,4 +57,6 @@ static void bootblock_mmu_init(void)
 	assert(!identity_map((uint32_t)_sram, _sram_size,
 						C0_ENTRYLO_COHERENCY_WB));
 	assert(!identity_map(dram_base, dram_size, C0_ENTRYLO_COHERENCY_WB));
+	assert(!identity_map((uint32_t)_soc_registers, _soc_registers_size,
+                                                C0_ENTRYLO_COHERENCY_UC));
 }