linux-user: remove --enable-guest-base/--disable-guest-base

All tcg host architectures now support the guest base and as
there is no real performance lost, it can be always enabled.

Anyway, guest base use can be disabled lively by setting guest
base to 0.

CONFIG_USE_GUEST_BASE is defined as (USE_GUEST_BASE && USER_ONLY),
it should have to be replaced by CONFIG_USER_ONLY in non CONFIG_USER_ONLY
parts, but as some other parts are using !CONFIG_SOFTMMU I have chosen to
use !CONFIG_SOFTMMU instead.

Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <1440373328-9788-2-git-send-email-laurent@vivier.eu>
Signed-off-by: Richard Henderson <rth@twiddle.net>