arch/x86: Move max cpuid leaf function into arch/x86

This cpuid function (0) is same across Intel and AMD so having it in
arch/x86 seems like a good idea.

Change-Id: I38f1c40bceac38ed6428f74b08bf60b971644f5a
Signed-off-by: Andrey Petrov <anpetrov@fb.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36282
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>

src/arch/x86/include/arch/cpu.h

@@ -141,6 +141,11 @@ static inline unsigned int cpuid_edx(unsigned int op)
 	return edx;
 }
 
+static inline unsigned int cpuid_get_max_func(void)
+{
+	return cpuid_eax(0);
+}
+
 #define X86_VENDOR_INVALID    0
 #define X86_VENDOR_INTEL      1
 #define X86_VENDOR_CYRIX      2