soc/intel/xeon_sp/skx: Properly set up MTRR's

Don't depend on the MTRR setup left over from FSP-M ExitTempRam.

Change-Id: I299123b3cd3c37b4345102c20fda77bf261892a2
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48673
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Marc Jones <marc@marcjonesconsulting.com>

src/soc/intel/xeon_sp/skx/cpu.c

@@ -193,7 +193,8 @@ static void pre_mp_init(void)
 {
 	printk(BIOS_DEBUG, "%s: entry\n", __func__);
 
-	x86_setup_fixed_mtrrs();
+	x86_setup_mtrrs_with_detect();
+	x86_mtrr_check();
 }
 
 static void post_mp_init(void)