x86 setup: early cmdline parser handle boolean options

This patch extends the early commandline parser to support boolean options.
The current version in mainline only supports parsing "option=arg" value pairs.

With this it should be easy making other messages like "Uncompressing kernel"
honour the "quiet" parameter, too.

Signed-off-by: Roland Kletzing <devzero@web.de>
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>