PSCI: Build option to enable D-Caches early in warmboot

This patch introduces a build option to enable D-cache early on the CPU
after warm boot. This is applicable for platforms which do not require
interconnect programming to enable cache coherency (eg: single cluster
platforms). If this option is enabled, then warm boot path enables
D-caches immediately after enabling MMU.

Fixes ARM-Software/tf-issues#456

Change-Id: I44c8787d116d7217837ced3bcf0b1d3441c8d80e
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index e66f511..903363a 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -154,3 +154,9 @@
 
 # Build verbosity
 V				:= 0
+
+# Whether to enable D-Cache early during warm boot. This is usually
+# applicable for platforms wherein interconnect programming is not
+# required to enable cache coherency after warm reset (eg: single cluster
+# platforms).
+WARMBOOT_ENABLE_DCACHE_EARLY	:= 0