Kconfig: Add a new DISTRO_DEFAULTS Kconfig option

Kconfig: Add a new DISTRO_DEFAULTS Kconfig option

DISTRO_DEFAULTS is intended to mirror / replace
include/config_distro_defaults.h.

The intend is for boards which include this file to select this from
their Kconfig files and when moving setting to Kconfig which are #define-ed
in config_distro_defaults.h to select this from DISTRO_DEFAULTS so that
boards which have selected DISTRO_DEFAULTS will keep the same configuration
as before without needing any defconfig file changes.

The initial list of selected things matches all settings recently removed
from config_distro_defaults.h because they have been converted to Kconfig,
with the exception of CMD_ELF and CMD_NET, which have a default of y, if
the default of these ever changes they should be selected by DISTRO_DEFAULTS
too.

For testing and example purposes this commit also converts ARCH_SUNXI
to use DISTRO_DEFAULT instead of selecting everything it needs itself.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>