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>

Makefile.inc

@@ -72,6 +72,9 @@ classes-y := ramstage romstage bootblock smm smmstub cpu_microcode libverstage v
 # Add dynamic classes for rmodules
 $(foreach supported_arch,$(ARCH_SUPPORTED), \
 	    $(eval $(call define_class,rmodules_$(supported_arch),$(supported_arch))))
+# Provide a macro to determine environment for free standing rmodules.
+$(foreach supported_arch,$(ARCH_SUPPORTED), \
+	$(eval rmodules_$(supported_arch)-generic-ccopts += -D__RMODULE__))
 
 #######################################################################
 # Helper functions for math and various file placement matters.