cpu/x86/mp_init.c: Add mp_run_on_all_cpus_synchronously

MTRR is a core level register which means 2 threads in one core share
same MTRR. There is a race condition could happen that AP overrides
BSP MTRR unintentionally.

In order to prevent such race condition between BSP and APs, this
patch provides a function to let BSP assign tasks to all APs and wait
them to complete the assigned tasks.

BUG=b:225766934

Change-Id: I8d1d49bca410c821a3ad0347548afc42eb860594
Signed-off-by: Kane Chen <kane.chen@intel.corp-partner.google.com>
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63566
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/x86/mp.h

@@ -117,6 +117,10 @@ enum cb_err mp_run_on_all_aps(void (*func)(void *), void *arg, long expire_us,
 /* Like mp_run_on_aps() but also runs func on BSP. */
 enum cb_err mp_run_on_all_cpus(void (*func)(void *), void *arg);
 
+/* Like mp_run_on_all_cpus but make sure all APs finish executing the
+   function call. The time limit on a function call is 1 second. */
+enum cb_err mp_run_on_all_cpus_synchronously(void (*func)(void *), void *arg);
+
 /*
  * Park all APs to prepare for OS boot. This is handled automatically
  * by the coreboot infrastructure.