x86/init: Fix cr4_init_shadow() on CR4-less machines

x86/init: Fix cr4_init_shadow() on CR4-less machines

cr4_init_shadow() will panic on 486-like machines without CR4.  Fix
it using __read_cr4_safe().

Reported-by: [email protected]
Signed-off-by: Andy Lutomirski <[email protected]>
Reviewed-by: Borislav Petkov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Fixes: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
Link: http://lkml.kernel.org/r/43a20f81fb504013bf613913dc25574b45336a61.1475091074.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>