pistachio: set correct CBMEM top address

This is required for proper dynamic CBMEM operation.

BRANCH=none
BUG=chrome-os-partner:31438
TEST=urara ramstage does not crash anymore in CBMEM initialization

Change-Id: Id8e001be20fc245c91b2639f89775e594b0de966
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Original-Commit-Id: b7c6e4090d76a172c269bff002428015cc8aac8a
Original-Change-Id: I5d44907443724891c8cff805208a7a3bb8e36752
Original-Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/232292
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9191
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/soc/imgtec/pistachio/cbmem.c

@@ -25,6 +25,5 @@
 
 void *cbmem_top(void)
 {
-	uintptr_t top = MIN(CONFIG_DRAM_SIZE_MB, 256) << 20;
-	return _dram + top;
+	return _dram + (CONFIG_DRAM_SIZE_MB << 20);
 }