build: update comment in configure.ac

For the time being at least, set the default to always enable a block
transfer blob interface.  Update the build comment to indicate this.

Change-Id: Icadb8735212066abee69a1d22c6fcbfccd9b6cee
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 4c056da..09fceb3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,7 +32,7 @@
 AS_IF([test "x$enable_static_layout" = "xyes"], [
     AX_APPEND_COMPILE_FLAGS([-DENABLE_STATIC_LAYOUT], [CXXFLAGS])
 ])
-# Enable BlockTransfer, P2A, and or LPC.
+# Enable P2A, and or LPC (block-transfer is always enabled).
 
 # Check/set gtest specific functions.
 PKG_CHECK_MODULES([GTEST], [gtest], [], [AC_MSG_NOTICE([gtest not found, tests will not build])])