x86/boot: Add a message about ignored early NMIs

Commit

  78a509fb

 ("x86/boot: Ignore NMIs during very early boot")

added an empty handler in early boot stage to avoid boot failure due to
spurious NMIs.

Add a diagnostic message to show that early NMIs have occurred.

  [ bp: Touchups. ]

  [ Committer note: tested by stopping the guest really early and
    injecting NMIs through qemu's monitor. Result:

    early console in setup code
    Spurious early NMIs ignored: 13
    ... ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Jun'ichi Nomura <junichi.nomura@nec.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/lkml/20231130103339.GCZWhlA196uRklTMNF@fat_crate.local