vboot: Remove get_sw_write_protect_state callback

We've just decided to remove the only known use of the VBSD_SW_WP flag
in vboot (https://chromium-review.googlesource.com/c/575389), since it
was unused and never reliable on all platforms anyway. Therefore, we can
now also remove the coreboot infrastructure that supported it. It
doesn't really hurt anyone, but removing it saves a small bit of effort
for future platforms.

Change-Id: I6706eba2761a73482e03f3bf46343cf1d84f154b
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/20628
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/baytrail/romstage/romstage.c

@@ -326,10 +326,3 @@ static void *setup_stack_and_mttrs(void)
 
 	return slot;
 }
-
-int get_sw_write_protect_state(void)
-{
-	u8 status;
-	/* Return unprotected status if status read fails. */
-	return (early_spi_read_wpsr(&status) ? 0 : !!(status & 0x80));
-}