arch/x86/postcar_loader: Add comment line for reloc_params assignment

During finalize_load(), cpu/x86/mtrr/earlymtrr.c:postcar_mtrr is signaled

to be loaded as reloc_params, e.g. with its cache flushed.

Add a comment line to specify the relationship to improve the readability.

I didn't see code to set up parameter at first time.
So, I just guess that adding a comment would be helpful. :)

Change-Id: Ic7d3f9cf514ce5a8efc2af9e78992cb39a91e537
Signed-off-by: NyeonWoo Kim <knw0507@naver.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86866
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Shuo Liu <shuo.liu@intel.com>

src/arch/x86/postcar_loader.c

@@ -83,7 +83,12 @@ void __noreturn prepare_and_run_postcar(void)
 
 static void finalize_load(uintptr_t *reloc_params, uintptr_t mtrr_frame_ptr)
 {
+	/*
+	 * set postcar(rmodule)'s parameter.
+	 * the parameter is defined as post_car_mtrrs in cpu/x86/mtrr/earlymtrr.c
+	 */
 	*reloc_params = mtrr_frame_ptr;
+
 	/*
 	 * Signal to rest of system that another update was made to the
 	 * postcar program prior to running it.