haswell: Make copy_spd a weak function

Instead of using function pointers, we can use weak functions. So, drop
the pointer from `romstage_params`, leaving `pei_data` as the only
remaining member. This will be cleaned up in a follow-up commit.

Change-Id: I3b17d21ea7a650734119a5cab4892fcb158b589d
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43105
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/mainboard/intel/baskingridge/romstage.c

@@ -114,7 +114,6 @@ void mainboard_romstage_entry(void)
 
 	struct romstage_params romstage_params = {
 		.pei_data = &pei_data,
-		.copy_spd = NULL,
 	};
 
 	/* Call into the real romstage main with this board's attributes. */