x86/setup: Parse the builtin command line before merging

Commit in Fixes was added as a catch-all for cases where the cmdline is
parsed before being merged with the builtin one.

And promptly one issue appeared, see Link below. The microcode loader
really needs to parse it that early, but the merging happens later.

Reshuffling the early boot nightmare^W code to handle that properly would
be a painful exercise for another day so do the chicken thing and parse the
builtin cmdline too before it has been merged.

Fixes: 0c40b1c7 ("x86/setup: Warn when option parsing is done too early")
Reported-by: Mike Lothian <mike@fireburn.co.uk>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240730152108.GAZqkE5Dfi9AuKllRw@fat_crate.local
Link: https://lore.kernel.org/r/20240722152330.GCZp55ck8E_FT4kPnC@fat_crate.local