dts: STM32MP13: ETH, SAI signals and UART fix

MP13: Eth (extended) signals addition
MP13: SAI signals addition
MP13: Update drive/bias prop on USART signals

The fact that these MP13 signals/updates were missing is a consequence
of a race between MP13 introductions and previous PRs.
They should have already been available.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>