dt-bindings: mfd: Add mp2733 compatible

Add new compatible for mp2733 mfd driver.

Signed-off-by: Saravanan Sekar <sravanhome@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220615145357.2370044-3-sravanhome@gmail.com