x86: xen: remove STACK_FRAME_NON_STANDARD from xen_cpuid

Since commit 4d65adfc ("x86: xen: insn: Decode Xen and KVM
emulate-prefix signature"), objtool is able to correctly parse the
prefixed instruction in xen_cpuid and emit correct orc unwind
information. Hence, marking the function as STACKFRAME_NON_STANDARD is
no longer needed.

This commit is basically a revert of commit 983bb6d2 ("x86/xen: Mark
xen_cpuid() stack frame as non-standard").

Signed-off-by: Maximilian Heyne <mheyne@amazon.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
CC: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20220517162425.100567-1-mheyne@amazon.de


Signed-off-by: Juergen Gross <jgross@suse.com>