arch: st_stm32: Remove I2C and SPI instances from common defconfig

Remove I2C and SPI instances when enabling I2C_STM32 and
SPI_STM32 drivers.

It allows to enable the drivers if ports I2C_4, SPI_4,
SPI_5, SPI_6 are selected.

Signed-off-by: Yannis Damigos <giannis.damigos@gmail.com>