x86 setup: add missing prototype; formatting fix

Add prototype for cmdline_find_option_bool() missing from:

    x86 setup: early cmdline parser handle boolean options

Also, fix up a minor formatting error in that patch.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>