rmodule: use program.ld for linking

Bring rmodule linking into the common linking method.
The __rmodule_entry symbol was removed while using
a more common _start symbol. The rmodtool will honor
the entry point found within the ELF header. Add
ENV_RMODULE so that one can distinguish the environment
when generating linker scripts for rmodules. Lastly,
directly use program.ld for the rmodule.ld linker script.

BUG=chrome-os-partner:44827
BRANCH=None
TEST=Built rambi and analyzed the relocatable ramstage,
     sipi_vector, and smm rmodules.

Change-Id: Iaa499eb229d8171272add9ee6d27cff75e7534ac
Signed-off-by: Aaron Durbin <adubin@chromium.org>
Reviewed-on: http://review.coreboot.org/11517
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/include/memlayout.h b/src/include/memlayout.h
index f67753c..09be615 100644
--- a/src/include/memlayout.h
+++ b/src/include/memlayout.h
@@ -43,9 +43,9 @@
 #define ARCH_STAGE_HAS_BSS_SECTION 1
 #endif
 
-/* Default is that currently ramstage and smm only has a heap. */
+/* Default is that currently ramstage, smm, and rmodules have a heap. */
 #ifndef ARCH_STAGE_HAS_HEAP_SECTION
-#define ARCH_STAGE_HAS_HEAP_SECTION (ENV_RAMSTAGE || ENV_SMM)
+#define ARCH_STAGE_HAS_HEAP_SECTION (ENV_RAMSTAGE || ENV_SMM || ENV_RMODULE)
 #endif
 
 #define STR(x) #x