baseboard/kukui: separate configs for stm32 and ite chips.
baseboard/kukui: separate configs for stm32 and ite chips.

This change pulls stm32 chip-specific options into
VARIANT_KUKUI_EC_STM32F098 (include save flash space operations),
and enable it83xx chip-specific options for it81202.

BUG=none
BRANCH=none
TEST=-buildall.
     -boot to kernel on juniper.
     -boot to manual recovery on icarus.

Signed-off-by: Dino Li <338d523ecf3700bd86eb9c34d220f91911d2a18c@ite.com.tw>
Change-Id: I81fb318960bf24780c164d9abe631ef70a360bf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2717344
Reviewed-by: Eric Yilun Lin <2f2733c7206ea2b76bd2db1905cc5e8a75841c48@chromium.org>

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