mfd: tps80031: Remove driver

Driver was upstreamed in 2013 and never got a user, remove it.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211021192258.21968-4-digetx@gmail.com