cr50: allocate signature headers in both RO and RW images

With the proper RO in place, RW must be signed in the same manner, as
RO. This patch makes sure that there is room in the RW header for the
signature.

BRANCH=none
BUG=chrome-os-partner:43025
TEST=with the rest of the patches applies the RO successfully boots up
     the RW.

Change-Id: I1538195e0181c23c874ddd300887cf5da8c5a867
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/311421
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

chip/g/config_chip.h

@@ -25,6 +25,7 @@
 #define CONFIG_PROGRAM_MEMORY_BASE     0x40000
 #define CONFIG_FLASH_SIZE              (512 * 1024)
 #define CONFIG_RO_HEAD_ROOM	       1024	/* Room for ROM signature. */
+#define CONFIG_RW_HEAD_ROOM	       CONFIG_RO_HEAD_ROOM  /* same for RW */
 
 /* Memory-mapped internal flash */
 #define CONFIG_INTERNAL_STORAGE

core/cortex-m/ec.lds.S

@@ -66,6 +66,9 @@ SECTIONS
     .text : {
 #if defined(SECTION_IS_RO) && defined(CONFIG_RO_HEAD_ROOM)
 	. = . +  CONFIG_RO_HEAD_ROOM;
+#endif
+#if defined(SECTION_IS_RW) && defined(CONFIG_RW_HEAD_ROOM)
+	. = . +  CONFIG_RW_HEAD_ROOM;
 #endif
         OUTDIR/core/CORE/init.o (.text.vecttable)
         . = ALIGN(4);