soc/intel/common/cpu: Use SoC overrides to get CPU privilege level

This patch implements a SoC overrides to check CPU privilege level
as the MSR is not consistent across platforms.

For example: On APL/GLK/DNV, it's MSR 0x120 and CNL onwards it's MSR
0x151.

BUG=b:211573253, b:211950520

Signed-off-by: Subrata Banik <subratabanik@google.com>
Change-Id: I515f0a3548bc5d6250e30f963d46f28f3c1b90b3
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60900
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/soc/intel/apollolake/cpu.c

@@ -47,6 +47,14 @@ static const struct reg_script core_msr_script[] = {
 	REG_SCRIPT_END
 };
 
+bool cpu_soc_is_in_untrusted_mode(void)
+{
+	msr_t msr;
+
+	msr = rdmsr(MSR_POWER_MISC);
+	return !!(msr.lo & ENABLE_IA_UNTRUSTED);
+}
+
 void soc_core_init(struct device *cpu)
 {
 	/* Configure Core PRMRR for SGX. */