x86/boot: Add error_putdec() helper

Add a helper to print decimal numbers to early console.

Suggested-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Jun'ichi Nomura <junichi.nomura@nec.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/lkml/20240123112624.GBZa-iYP1l9SSYtr-V@fat_crate.local/
Link: https://lore.kernel.org/r/20240202035052.17963-1-junichi.nomura@nec.com