x86: Honor 'quiet' command line option in real mode boot decompressor.

This patch lets the early real mode code look for the 'quiet' option
on the kernel command line and pass a loadflag to the decompressor.
When this flag is set, we suppress the "Decompressing Linux... Parsing
ELF... done." messages.

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>