x86: garbage collect SMM programs

The non-module SMM programs were not being garbage collected
during linking. Do this so that one doesn't have to add dependencies
for unused functions in SMM.

TEST=Interrogated readelf -e smm.elf on both builds as well as diffed
     the symbol table. Runtime testing was not done.

Change-Id: I31991496d92191e540df6340c587eec09c7022b3
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10219
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/cpu/x86/smm/Makefile.inc

@@ -82,7 +82,7 @@ endif
 else # CONFIG_SMM_MODULES
 
 $(obj)/cpu/x86/smm/smm_wrap: $(obj)/cpu/x86/smm/smm.o $(src)/cpu/x86/smm/$(SMM_LDSCRIPT)
-	$(LD_smm) $(SMM_LDFLAGS) -nostdlib -nostartfiles -static -o $(obj)/cpu/x86/smm/smm.elf -T $(src)/cpu/x86/smm/$(SMM_LDSCRIPT) $(obj)/cpu/x86/smm/smm.o
+	$(LD_smm) $(SMM_LDFLAGS) -nostdlib -nostartfiles --gc-sections -static -o $(obj)/cpu/x86/smm/smm.elf -T $(src)/cpu/x86/smm/$(SMM_LDSCRIPT) $(obj)/cpu/x86/smm/smm.o
 	$(NM_smm) -n $(obj)/cpu/x86/smm/smm.elf | sort > $(obj)/cpu/x86/smm/smm.map
 	$(OBJCOPY_smm) -O binary $(obj)/cpu/x86/smm/smm.elf $(obj)/cpu/x86/smm/smm
 

src/cpu/x86/smm/smm.ld

@@ -48,7 +48,7 @@ SECTIONS
 	 */
 	. = 0xa8000 - (( CPUS - 1) * 0x400);
 	.jumptable : {
-		*(.jumptable)
+		KEEP(*(.jumptable));
 	}
 
 	/DISCARD/ : {

src/cpu/x86/smm/smm_tseg.ld

@@ -19,7 +19,7 @@ SECTIONS
 	 */
 	. = 0x8000 - (( CPUS - 1) * 0x400);
 	.jumptable : {
-		*(.jumptable)
+		KEEP(*(.jumptable));
 	}
 
 	/* Data used in early SMM TSEG handler. */