cpu/intel/fit: Reserve the FIT pointer using a .c file

No need to do this assembly anymore.

Change-Id: I69b42c31e495530fe96030a5a25209775f9d4dca
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51533
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/cpu/intel/fit/Makefile.inc

@@ -1,4 +1,4 @@
-bootblock-y += fit.S
+bootblock-y += fit.c
 
 # The FIT table is generated as a separate CBFS file.
 # The FIT pointer is reserved in fit.c and updated to point to the 'intel_fit'

src/cpu/intel/fit/fit.c

@@ -1,9 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-.section ".fit_pointer", "a", @progbits
-	.code32
+#include <stdint.h>
+
 /* This will get updated by ifittool later on to point to the cbfs 'intel_fit' file. */
-.global fit_pointer
-fit_pointer:
-.long 0
-.long 0
+__attribute__((used, __section__(".fit_pointer"))) const uint64_t fit_ptr = 0;