i2c3 and uart4 are available on the GPIO header. Though these pins only
have this one special function, the user may choose to use them as GPIOs
instead.

Since our policy is not to choose what function to present on the GPIO
headers of development boards, remove them.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>