efi/x86: Support builtin command line

Add support for the x86 CMDLINE_BOOL and CMDLINE_OVERRIDE configuration
options.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200430182843.2510180-11-nivedita@alum.mit.edu


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>