x86: Support booting SeaBIOS

x86: Support booting SeaBIOS

SeaBIOS is an open source implementation of a 16-bit x86 BIOS.
It can run in an emulator or natively on x86 hardware with the
use of coreboot. With SeaBIOS's help, we can boot some OSes
that require 16-bit BIOS services like Windows/DOS.

As U-Boot, we have to manually create a table where SeaBIOS gets
system information (eg: E820) from. The table unfortunately has
to follow the coreboot table format as SeaBIOS currently supports
booting as a coreboot payload.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>