ARM: dts: stm32: adjust USB OTG gadget fifo sizes in stm32mp151

Defaut use case on stm32mp151 USB OTG is ethernet gadget, using EP1 bulk
endpoint (MPS=512 bytes) and EP2 interrupt endpoint (MPS=16 bytes).
This patch optimizes USB OTG FIFO sizes accordingly.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>