x86/microcode: Make reload_early_microcode() static

fe055896 ("x86/microcode: Merge the early microcode loader") left this
needlessly public. Git archaeology provided by Borislav.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230812195727.834943153@linutronix.de