ARM: dts: clps711x: Add keypad node

This adds missing keypad node to basic clps711x DT.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Link: https://lore.kernel.org/r/20210405051658.26779-2-shc_work@mail.ru

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