arch/x86: always use _start as entry symbol for all stages

Instead of keeping track of all the combinations of entry points
depending on the stage and other options just use _start. That way,
there's no need to update the arch/header.ld for complicated cases
as _start is always the entry point for a stage.

Change-Id: I7795a5ee1caba92ab533bdb8c3ad80294901a48b
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/13882
Tested-by: build bot (Jenkins)
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>

src/arch/x86/include/arch/header.ld

@@ -20,27 +20,4 @@ PHDRS
 	to_load PT_LOAD;
 }
 
-/*
- * For CONFIG_SEPARATE_VERSTAGE romstage doesn't have the cache-as-ram setup.
- * It only contains the teardown code. The verstage has the cache-as-ram setup
- * code. Therefore, it needs the protected_start symbol as its entry point.
- * The romstage entry will be named _start for consistency, but it's likely
- * to be implemented in the chipset code in order to control the logic flow.
- */
-#if IS_ENABLED(CONFIG_SEPARATE_VERSTAGE)
-	#if ENV_RAMSTAGE || ENV_RMODULE || ENV_ROMSTAGE
-	ENTRY(_start)
-	#elif ENV_VERSTAGE
-	ENTRY(protected_start)
-	#endif
-#else
-	#if ENV_RAMSTAGE || ENV_RMODULE
-	ENTRY(_start)
-	#elif ENV_ROMSTAGE
-	ENTRY(protected_start)
-	#endif
-#endif
-
-#if IS_ENABLED(CONFIG_C_ENVIRONMENT_BOOTBLOCK) && ENV_BOOTBLOCK
 ENTRY(_start)
-#endif