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>

src/arch/arm64/include/arch/header.ld

@@ -17,6 +17,8 @@
  * Foundation, Inc.
  */
 
+#include <rules.h>
+
 /* We use ELF as output format. So that we can debug the code in some form. */
 OUTPUT_FORMAT("elf64-littleaarch64", "elf64-littleaarch64", "elf64-littleaarch64")
 OUTPUT_ARCH(aarch64)
@@ -26,7 +28,13 @@ PHDRS
 	to_load PT_LOAD;
 }
 
-#ifdef __BOOTBLOCK__
+#if ENV_BOOTBLOCK
 TARGET(binary)
 #endif
+
+/* secmon uses rmodules */
+#if ENV_RMODULE
+ENTRY(_start)
+#else
 ENTRY(stage_entry)
+#endif

src/arch/arm64/stage_entry.S

@@ -136,12 +136,12 @@ ENDPROC(arm64_c_environment)
 	2002:
 .endm
 
-ENTRY(__rmodule_entry)
+ENTRY(_start)
 	split_bsp_path
 	/* Save the arguments to secmon in x25 */
 	mov	x25, x0
 	b	arm64_c_environment
-ENDPROC(__rmodule_entry)
+ENDPROC(_start)
 
 /*
  * Setup SCTLR so that: