urara: Identity map DRAM/SRAM

Using identity_map(), map the DRAM/SRAM regions to themselves (which
happens to be using KUSEG on urara).

The bootblock (which still runs in KSEG0) sets up the identity mapping
in bootblock_mmu_init() so that ROM/RAM stages can be loaded into the
KUSEG address range.

The stack and pre-RAM CBMEM console also remain in KSEG0 since we
don't really care about their physical addresses.

Also splitting CBFS cache to pre and post RAM, to allow for larger
rambase images.

BUG=chrome-os-partner:36258
BRANCH=none
TEST=With the rest of coreboot and depthcharge patches applied:
    - booted urara into the kernel login prompt
    - from depthcharge CLI tried accessing memory below 0x100000 -
      observed the exception.

Change-Id: If78f1c5c54d3587fe83e25c79698b2e9e41d3309
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 9668b440b35805e8ce442be62f67053cedcb205e
Original-Change-Id: I187d02fa2ace08b9fb7a333c928e92c54465abc2
Original-Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/246694
Reviewed-on: http://review.coreboot.org/9816
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/mips/bootblock_simple.c

@@ -32,5 +32,7 @@ void main(void)
 	console_init();
 #endif
 
+	bootblock_mmu_init();
+
 	run_romstage();
 }