ARM: multi_v7_defconfig: add STM32 CEC support

Enable CEC support for STMicroelectronics as loadable module.

Signed-off-by: Yannick Fertre <yannick.fertre@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Link: https://lore.kernel.org/r/20210129084842.29123-1-alexandre.torgue@foss.st.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>