zephyr: ioex: Fix compile error when cros ioex drivers disabled
zephyr: ioex: Fix compile error when cros ioex drivers disabled

The link fails when the following Kconfig options are set:
    CONFIG_PLATFORM_EC_IOEX=y
    CONFIG_PLATFORM_EC_IOEX_CROS_DRV=n

Stub out the ioex_config[] array for this configuration.

BUG=none
BRANCH=none
TEST=Using next CL, verify herobrine_npcx9 compile when enabling an
upstream Zephyr IOEX driver.

Signed-off-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Change-Id: I1db49fe30374b2fe329d42c9568a94ee0607e3a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3344029
Reviewed-by: Aaron Massey <79529a820df71f45023239a3663736629646cc34@google.com>
Reviewed-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec