libpayload: Change CONFIG_X86_SERIAL_CONSOLE to CONFIG_8250_SERIAL_CONSOLE

While the 8250 compatible serial port driver is primarily useful on x86
systems because it works with the legacy x86 com ports, some devices which
aren't x86 based have 8250 compatible UARTs as well. This change renames the
CONFIG_X86_SERIAL_CONSOLE option to the more general and direct
CONFIG_8250_SERIAL_CONSOLE and fixes up the dependencies so that non-x86
systems can enable the driver, although it will default to on on x86 and off
otherwise.

Also, the default IO port address that's added to the sysinfo structure on x86
and which is intended to be overwritten by a value in the coreboot tables is
not used on ARM. That variable is adjusted so that it's more clear it's a
default value, and made dependent on x86 since that's the only place its value
is actually used.

Change-Id: Ifeaade0e7bd76d382426e947275a9c933da4930e
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/170834
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 9a10e39a2da3cb0bfb316c0869cf5025078e287f)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6655
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>