omapl138_lcdk_defconfig: don't build support for SPI

omapl138_lcdk_defconfig: don't build support for SPI

The following warning is emited when building u-boot for da850-lcdk:

===================== WARNING ======================
This board does not use CONFIG_DM_SPI. Please update
the board before v2019.04 for no dm conversion
and v2019.07 for partially dm converted drivers.
Failure to update can lead to driver/board removal
See doc/driver-model/MIGRATION.txt for more info.
====================================================
===================== WARNING ======================
This board does not use CONFIG_DM_SPI_FLASH. Please update
the board to use CONFIG_SPI_FLASH before the v2019.07 release.
Failure to update by the deadline may result in board removal.
See doc/driver-model/MIGRATION.txt for more info.
====================================================

While we could fix it by selecting CONFIG_DM_SPI, there's no need to
build it at all as SPI is disabled on da850-lcdk. Remove all unneeded
options from the defconfig.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Heiko Schocher <hs@denx.de>