x86/microcode/intel: replace sync_core() with native_cpuid_reg(eax)

BugLink: https://bugs.launchpad.net/bugs/1875905

On Intel it is required to do CPUID(1) before reading the microcode
revision MSR. Current code in 4.4 an 4.9 relies on sync_core() to call
CPUID, unfortunately on 32 bit machines code inside sync_core() always
jumps past CPUID instruction as it depends on data structure boot_cpu_data
witch are not populated correctly so early in boot sequence.

It depends on:
commit 5dedade6 ("x86/CPU: Add native CPUID variants returning a single
datum")

This patch is for 4.4 but also should apply to 4.9
Signed-off-by: Evalds Iodzevics <evalds.iodzevics@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/include/asm/microcode_intel.h

@@ -60,7 +60,7 @@ static inline u32 intel_get_microcode_revision(void)
 	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
-	sync_core();
+	native_cpuid_eax(1);
 
 	/* get the current revision from MSR 0x8B */
 	native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);